diff --git a/.env.example b/.env.example
index a7ffd18..4088536 100644
--- a/.env.example
+++ b/.env.example
@@ -5,6 +5,9 @@
 # --- App ---
 BOR_ENVIRONMENT=development
 # BOR_APP_NAME=Brain of Reese      # display name on all pages — titles, header brand, status labels, aria text (phase 39)
+# BOR_INPUT_PLACEHOLDER=Ask me anything…   # composer placeholder, chat page (phase 62)
+# BOR_FOOTER_TEXT=Powered by self-hosted models   # footer line on every page (phase 62)
+# BOR_THEME=            # filename under frontend/assets/themes/ (e.g. indigo.css) — overrides the built-in palette; empty = built-in (phase 62)
 # BOR_LOG_LEVEL=INFO
 # BOR_STATIC_DIR=frontend          # dev default; container sets /app/static
 
diff --git a/Containerfile b/Containerfile
index 70b21a1..6bda853 100644
--- a/Containerfile
+++ b/Containerfile
@@ -26,6 +26,7 @@ RUN mkdir -p /out/assets \
     && esbuild ./assets/brand.js   --minify --outfile=/out/assets/brand.js \
     && esbuild ./assets/markdown.js --minify --outfile=/out/assets/markdown.js \
     && esbuild ./assets/styles.css  --minify --outfile=/out/assets/styles.css \
+    && cp -r ./assets/themes /out/assets/themes \
     && cp ./index.html ./sources.html ./document.html ./login.html ./tuning.html ./git-sources.html ./history.html ./shared.html ./doc-edit.html /out/
 
 # ---------- Stage 2: python dependencies ----------
diff --git a/README.md b/README.md
index d988af8..6d48791 100644
--- a/README.md
+++ b/README.md
@@ -732,6 +732,9 @@ served locally (no CDN), `BOR_ENVIRONMENT=production`.
 | Env | Default | Meaning |
 |-----|---------|---------|
 | `BOR_APP_NAME` | `Brain of Reese` | the display name everywhere (phase 39): every page `<title>`, the header brand, the chat status labels ("… is thinking"), the empty-state greeting, and the aria/placeholder text. Served to the frontend by `GET /api/config` and applied by `assets/brand.js`; a name starting `Brain of ` keeps the bold split (`Brain of <strong>rest</strong>`), any other name renders in normal weight. Unset ⇒ byte-identical to the default |
+| `BOR_INPUT_PLACEHOLDER` | `Ask me anything…` | the chat composer placeholder (`#message-input`, chat page only); applied by `assets/brand.js` from `GET /api/config`; unset ⇒ the template default |
+| `BOR_FOOTER_TEXT` | `Powered by self-hosted models` | the footer line on all 9 pages (the `.footer-text` spans); same mechanism; unset ⇒ the template default |
+| `BOR_THEME` | *(empty)* | a filename under `frontend/assets/themes/` (e.g. `indigo.css`) — a `:root` palette override injected after `styles.css` (later wins the cascade); the server refuses a malformed name at startup (bare `^[a-z0-9_-]+\.css$` filename); a missing file degrades to the built-in theme; unset ⇒ the built-in dark-tech palette |
 | `BOR_DATABASE_URL` | local compose URL | SQLAlchemy URL (psycopg) |
 | `BOR_LLM_BASE_URL` | `https://aipi.reeseapps.com/v1` | OpenAI-compatible endpoint |
 | `BOR_LLM_API_KEY` | — (falls back to `$AIPI_KEY`) | aipi API key |
@@ -761,6 +764,21 @@ served locally (no CDN), `BOR_ENVIRONMENT=production`.
 | `DEBUGPY` | `0` | `1` ⇒ attach-on-demand debugpy on `DEBUGPY_PORT` (default 5678) |
 | `BOR_LOG_LEVEL` | `INFO` | app log level |
 
+### Customizing the look
+
+The app ships as “Brain of Reese”, but every identity string is an env
+var: `BOR_APP_NAME` (display name), `BOR_INPUT_PLACEHOLDER` (chat composer
+placeholder), and `BOR_FOOTER_TEXT` (the footer line on every page) — all
+served by `GET /api/config` and applied by `assets/brand.js` at boot.
+Color themes are plain CSS variable overrides: write a `:root` block in
+`frontend/assets/themes/` and point `BOR_THEME` at the filename
+([the themes `README.md`](frontend/assets/themes/README.md) is the
+authoring guide, `indigo.css` the working example). The server refuses a
+malformed `BOR_THEME` at startup, and a missing theme file degrades to the
+built-in palette — the page never breaks. Leave everything unset and the
+app renders the defaults byte-identically: the dark-tech palette shown
+throughout this README is the no-config default.
+
 ## Troubleshooting
 
 - **`401` from aipi** — set `BOR_LLM_API_KEY` (or `$AIPI_KEY`).
diff --git a/app/api/config.py b/app/api/config.py
index 7d2f061..95d47c6 100644
--- a/app/api/config.py
+++ b/app/api/config.py
@@ -1,5 +1,7 @@
 """Public app metadata (display name + version) for the frontend brand
-layer, plus the phase-59 docs-push flag (the "Save as doc" gating)."""
+layer, the phase-59 docs-push flag (the "Save as doc" gating), and the
+phase-62 UI customization strings (composer placeholder, footer line,
+theme file name)."""
 from __future__ import annotations
 
 from fastapi import APIRouter, Depends
@@ -12,12 +14,18 @@ router = APIRouter(tags=["config"])
 @router.get("/config")
 def app_config(settings: Settings = Depends(get_settings)) -> dict[str, str | bool]:  # noqa: B008
     """Public app metadata for the frontend brand layer (phase 39) +
-    the phase-59 ``docs_repo_configured`` flag — the chat page's
-    "Save as doc" button gating, surfaced the way ``app_name`` is
-    (the SAME boot fetch, no new network surface). Inert false while
-    ``BOR_DOCS_REPO`` is empty (the feature is off, D3)."""
+    the phase-59 ``docs_repo_configured`` flag + the phase-62 UI
+    customization keys (``input_placeholder``, ``footer_text``,
+    ``theme``) — all display strings, the SAME boot fetch (no new
+    network surface) and the same public posture as ``app_name``
+    (no secrets). Values are passed through verbatim: the frontend
+    brand layer treats an empty string as "keep the template default"
+    (the unset => byte-identical contract)."""
     return {
         "app_name": settings.app_name,
         "version": settings.app_version,
         "docs_repo_configured": settings.docs_configured,
+        "input_placeholder": settings.input_placeholder,
+        "footer_text": settings.footer_text,
+        "theme": settings.theme,
     }
diff --git a/app/config.py b/app/config.py
index 06fddf5..6576073 100644
--- a/app/config.py
+++ b/app/config.py
@@ -46,6 +46,15 @@ class Settings(BaseSettings):
     log_level: str = "INFO"
     static_dir: str = "frontend"
 
+    # --- UI customization (phase 62, TODO L3) ---
+    # Defaults are the phase-61 neutral copy — UNSET => byte-identical UI.
+    input_placeholder: str = "Ask me anything…"
+    footer_text: str = "Powered by self-hosted models"
+    #: Theme file NAME under frontend/assets/themes/ (e.g. "indigo.css");
+    #: empty = the built-in dark-tech palette. Validated: bare filename
+    #: only — no paths, no ".." (no-CDN: served from the static dir).
+    theme: str = ""
+
     # --- Database (PostgreSQL 17 + pgvector) ---
     database_url: str = "postgresql+psycopg://reese:reese@localhost:5432/brain_of_reese"
 
@@ -202,6 +211,27 @@ class Settings(BaseSettings):
     #: separate from ``sources_dir`` (the source checkouts).
     docs_work_dir: str = "~/bor-docs"
 
+    @field_validator("theme", mode="after")
+    @classmethod
+    def _theme_bare_css_filename(cls, v: str) -> str:
+        r"""Phase 62 (A5): the theme is a FILE NAME under
+        ``frontend/assets/themes/``, served from the static dir
+        (no-CDN) — so only a bare lowercase ``.css`` filename is legal
+        (``^[a-z0-9_-]+\.css$``). Anything else (a path, ``..``,
+        uppercase, a missing extension) is a typo that would silently
+        404 at runtime — fail loudly at startup instead, naming the
+        offending value and the allowed shape (the phase-56 fail-loud
+        house style)."""
+        if v == "":
+            return v  # empty = the built-in dark-tech palette
+        if re.fullmatch(r"[a-z0-9_-]+\.css", v) is None:
+            raise ValueError(
+                "theme must be a bare .css filename under "
+                "frontend/assets/themes/ (lowercase letters/digits/"
+                f"'_'/'-', e.g. 'indigo.css') — got {v!r}"
+            )
+        return v
+
     @field_validator("import_extensions")
     @classmethod
     def _import_extensions_known(cls, v: str) -> str:
diff --git a/frontend/assets/brand.js b/frontend/assets/brand.js
index 0189e13..ca13094 100644
--- a/frontend/assets/brand.js
+++ b/frontend/assets/brand.js
@@ -31,13 +31,42 @@
  *          skipped so page source is never mutated;
  *       4. an attribute pass — the aria-label / placeholder / meta
  *          content attributes containing the literal (the #messages
- *          aria-label, the input label, the meta descriptions).
+ *          aria-label, the input label, the meta descriptions);
+ *       5–7. Phase 62 (owner-locked 2026-09-01, TODO L3) — the SAME
+ *          settled config also carries the three UI-customization
+ *          keys, applied in this same .then, AFTER the app_name
+ *          passes and INDEPENDENT of them (they apply even when the
+ *          name is the default/empty). Each empty value is a no-op —
+ *          an unset deployment stays byte-identical:
+ *          5. input_placeholder — non-empty → the #message-input
+ *             placeholder (the chat page only; every other page
+ *             no-ops via the null guard);
+ *          6. footer_text — non-empty → every .footer-text node's
+ *             textContent (all 9 pages, the phase-61 hook; an
+ *             operator string can't inject markup via textContent);
+ *          7. theme — non-empty → a <link rel="stylesheet"> inserted
+ *             IMMEDIATELY AFTER the styles.css link (the theme's
+ *             :root overrides win by cascade order). The styles.css
+ *             finder matches the RAW attribute path with any query/
+ *             fragment stripped — the phase-33/54 cache-busting
+ *             middleware serves the HTML with the asset refs rewritten
+ *             to "…/styles.css?v=<token>", and el.href (the absolute
+ *             URL) would never end with "styles.css" once versioned.
+ *             The filename is validated server-side (a bare *.css
+ *             name — no path can reach here via /api/config); a
+ *             MISSING file degrades to the built-in theme (onerror →
+ *             console.warn — A5, the page never breaks). Guarded by
+ *             #theme-override: never inserted twice.
  *   • fetch failure / empty name → the default stays + console.warn
  *     (the loadHealth house style: progressive enhancement, the page
  *     never breaks).
  *
- * No-op property: with BOR_APP_NAME unset the /api/config answer IS the
- * literal, so every replacement below is a byte-identical no-op.
+ * No-op property: with the customization env vars (BOR_APP_NAME,
+ * BOR_INPUT_PLACEHOLDER, BOR_FOOTER_TEXT, BOR_THEME) unset, /api/config
+ * answers with the template defaults themselves — the name IS the
+ * literal, the placeholder and footer are the phase-61 copy (re-setting
+ * them is invisible), the theme is empty (the link is skipped) — so an
+ * unset deployment renders byte-identical.
  */
 
 /* The synchronous default — set BEFORE any fetch, so module scripts
@@ -90,65 +119,135 @@ window.BOR_CONFIG_PROMISE = BOR_CONFIG_PROMISE;
 function applyBrand() {
   BOR_CONFIG_PROMISE.then((cfg) => {
     const name = typeof cfg?.app_name === "string" ? cfg.app_name.trim() : "";
-    if (!name) return; // empty / missing: the default stands
-    window.BOR_BRAND = name;
+    if (name) {
+      // A configured name: apply it (empty / missing: the default
+      // stands — and the phase-62 keys below are INDEPENDENT of the
+      // name, so they still apply).
+      window.BOR_BRAND = name;
 
-    // 1. The document title (global replace of the literal — covers
-    //    every page's static "<…> · Brain of Reese" titles).
-    document.title = document.title.replaceAll(BRAND_LITERAL, name);
+      // 1. The document title (global replace of the literal — covers
+      //    every page's static "<…> · Brain of Reese" titles).
+      document.title = document.title.replaceAll(BRAND_LITERAL, name);
 
-    // 2. The header brand on every page: a name starting "Brain of "
-    //    keeps the bold split (the current look), anything else
-    //    renders plain — the name is always escaped.
-    for (const el of document.querySelectorAll(".brand-text")) {
-      if (name.startsWith("Brain of ")) {
-        const rest = name.slice("Brain of ".length);
-        el.innerHTML = `Brain of <strong>${escapeHTML(rest)}</strong>`;
-      } else {
-        el.textContent = name;
-      }
-    }
-
-    // 3. Prose: a TreeWalker over the body's text nodes replaces the
-    //    literal (the empty-state h1, any other copy). Text nodes
-    //    inside <script>/<style> are rejected — the page source must
-    //    never be rewritten.
-    const walker = document.createTreeWalker(
-      document.body,
-      NodeFilter.SHOW_TEXT,
-      {
-        acceptNode(node) {
-          const tag = node.parentElement ? node.parentElement.tagName : "";
-          return tag === "SCRIPT" || tag === "STYLE"
-            ? NodeFilter.FILTER_REJECT
-            : NodeFilter.FILTER_ACCEPT;
-        },
-      },
-    );
-    const nodes = [];
-    while (walker.nextNode()) nodes.push(walker.currentNode);
-    for (const node of nodes) {
-      if (node.nodeValue && node.nodeValue.includes(BRAND_LITERAL)) {
-        node.nodeValue = node.nodeValue.replaceAll(BRAND_LITERAL, name);
-      }
-    }
-
-    // 4. Attributes: the #messages aria-label, the composer input
-    //    label, the meta descriptions — aria-label / placeholder /
-    //    meta content only, each replaced in place.
-    for (const el of document.querySelectorAll(
-      "[aria-label], [placeholder], meta[content]",
-    )) {
-      for (const attr of ["aria-label", "placeholder"]) {
-        const v = el.getAttribute(attr);
-        if (v && v.includes(BRAND_LITERAL)) {
-          el.setAttribute(attr, v.replaceAll(BRAND_LITERAL, name));
+      // 2. The header brand on every page: a name starting "Brain of "
+      //    keeps the bold split (the current look), anything else
+      //    renders plain — the name is always escaped.
+      for (const el of document.querySelectorAll(".brand-text")) {
+        if (name.startsWith("Brain of ")) {
+          const rest = name.slice("Brain of ".length);
+          el.innerHTML = `Brain of <strong>${escapeHTML(rest)}</strong>`;
+        } else {
+          el.textContent = name;
         }
       }
-      if (el.tagName === "META") {
-        const v = el.getAttribute("content");
-        if (v && v.includes(BRAND_LITERAL)) {
-          el.setAttribute("content", v.replaceAll(BRAND_LITERAL, name));
+
+      // 3. Prose: a TreeWalker over the body's text nodes replaces the
+      //    literal (the empty-state h1, any other copy). Text nodes
+      //    inside <script>/<style> are rejected — the page source must
+      //    never be rewritten.
+      const walker = document.createTreeWalker(
+        document.body,
+        NodeFilter.SHOW_TEXT,
+        {
+          acceptNode(node) {
+            const tag = node.parentElement ? node.parentElement.tagName : "";
+            return tag === "SCRIPT" || tag === "STYLE"
+              ? NodeFilter.FILTER_REJECT
+              : NodeFilter.FILTER_ACCEPT;
+          },
+        },
+      );
+      const nodes = [];
+      while (walker.nextNode()) nodes.push(walker.currentNode);
+      for (const node of nodes) {
+        if (node.nodeValue && node.nodeValue.includes(BRAND_LITERAL)) {
+          node.nodeValue = node.nodeValue.replaceAll(BRAND_LITERAL, name);
+        }
+      }
+
+      // 4. Attributes: the #messages aria-label, the composer input
+      //    label, the meta descriptions — aria-label / placeholder /
+      //    meta content only, each replaced in place.
+      for (const el of document.querySelectorAll(
+        "[aria-label], [placeholder], meta[content]",
+      )) {
+        for (const attr of ["aria-label", "placeholder"]) {
+          const v = el.getAttribute(attr);
+          if (v && v.includes(BRAND_LITERAL)) {
+            el.setAttribute(attr, v.replaceAll(BRAND_LITERAL, name));
+          }
+        }
+        if (el.tagName === "META") {
+          const v = el.getAttribute("content");
+          if (v && v.includes(BRAND_LITERAL)) {
+            el.setAttribute("content", v.replaceAll(BRAND_LITERAL, name));
+          }
+        }
+      }
+    }
+
+    // Phase 62 (owner-locked 2026-09-01, TODO L3): the SAME settled
+    // config also carries the three customization keys — applied here,
+    // INDEPENDENT of the app_name block above (they apply even when
+    // the name is the default/empty). Each empty value is a no-op, so
+    // an unset deployment stays byte-identical (no attribute or
+    // element touched, no second network call).
+    const placeholder =
+      typeof cfg?.input_placeholder === "string" ? cfg.input_placeholder : "";
+    if (placeholder) {
+      // 5. The composer placeholder — the chat page only:
+      //    #message-input exists only on index.html, so every other
+      //    page no-ops via the null guard.
+      document.querySelector("#message-input")?.setAttribute(
+        "placeholder",
+        placeholder,
+      );
+    }
+
+    const footerText =
+      typeof cfg?.footer_text === "string" ? cfg.footer_text : "";
+    if (footerText) {
+      // 6. The footer line on every page (all 9 carry the phase-61
+      //    .footer-text hook). textContent on purpose: an operator
+      //    string can't inject markup.
+      document.querySelectorAll(".footer-text").forEach((el) => {
+        el.textContent = footerText;
+      });
+    }
+
+    const themeName = typeof cfg?.theme === "string" ? cfg.theme : "";
+    if (themeName) {
+      // 7. The theme stylesheet — a <link> inserted IMMEDIATELY AFTER
+      //    the existing styles.css link, so the theme's :root
+      //    overrides win by cascade order. The filename is validated
+      //    server-side (task 01: a bare *.css name) — no path input
+      //    can reach here via /api/config. Guarded by #theme-override:
+      //    never applied twice (the loadHealth house style — never
+      //    break the page, never double-apply). A missing file
+      //    degrades to the built-in theme (A5): the onerror warns,
+      //    nothing else.
+      if (!document.getElementById("theme-override")) {
+        // Phase 33/54: the served HTML may carry the cache-bust query
+        // (?v=<token>) on the asset ref — match on the RAW attribute
+        // path with query/fragment stripped, never on el.href (the
+        // absolute URL, which would include the token).
+        const stylesLink = Array.from(
+          document.querySelectorAll('link[rel="stylesheet"]'),
+        ).find((el) => {
+          const ref = (el.getAttribute("href") || "").split(/[?#]/)[0];
+          return ref.endsWith("styles.css");
+        });
+        if (stylesLink) {
+          const link = document.createElement("link");
+          link.rel = "stylesheet";
+          link.href = "/assets/themes/" + themeName;
+          link.id = "theme-override";
+          link.onerror = () =>
+            console.warn(
+              "brand: theme " + themeName +
+              " did not load — the built-in theme stands.",
+            );
+          stylesLink.insertAdjacentElement("afterend", link);
         }
       }
     }
diff --git a/frontend/assets/themes/README.md b/frontend/assets/themes/README.md
new file mode 100644
index 0000000..4e6ab13
--- /dev/null
+++ b/frontend/assets/themes/README.md
@@ -0,0 +1,77 @@
+# Themes — authoring guide (phase 62)
+
+A theme is a small CSS file that overrides the `:root` palette variables.
+That is the entire mechanism — no component CSS is theme-aware, every
+color in the app reads a `--*` variable, so a later stylesheet wins by
+cascade order.
+
+## How a theme loads
+
+1. Set `BOR_THEME=<file>` (a bare FILENAME, e.g. `BOR_THEME=indigo.css`).
+   `app/config.py` validates it at startup — anything not matching
+   `^[a-z0-9_-]+\.css$` (a path, `..`, uppercase, a missing extension)
+   refuses to boot, naming the value (the phase-56 fail-loud house
+   style).
+2. The value rides the existing boot fetch: `GET /api/config` →
+   `frontend/assets/brand.js` inserts
+   `<link rel="stylesheet" href="/assets/themes/<file>">` IMMEDIATELY
+   AFTER the `styles.css` link — later wins the cascade.
+3. A theme file MISSING at runtime (typo past the validator, or the file
+   deleted after the image was built) degrades to the built-in theme —
+   `brand.js` warns in the console, the page never breaks (the
+   loadHealth house style, A5).
+4. UNSET (`BOR_THEME` empty) ⇒ no link is inserted at all — the
+   deployment renders byte-identical to the built-in dark-tech palette.
+   Loading is opt-in via the env var, never by directory scanning.
+
+## The variables
+
+A theme overrides the **8 identity variables** in a single `:root` block.
+Built-in values (from `frontend/assets/styles.css`) for reference:
+
+| Variable       | Built-in   | Role                                                        |
+| -------------- | ---------- | ----------------------------------------------------------- |
+| `--bg`         | `#0f0a0a`  | page background (text on it: `--ink`)                       |
+| `--surface`    | `#1a0f0f`  | cards, panels, code blocks (text on it: `--ink`)            |
+| `--ink`        | `#f0e6e6`  | primary text                                                |
+| `--ink-soft`   | `#b8a8a8`  | secondary text (5.1:1 on `--surface`)                       |
+| `--line`       | `#2d1a1a`  | decorative 1px borders (no contrast obligation)             |
+| `--brand`      | `#f43f5e`  | brand accent — buttons, links (text ON it is `--bg`)        |
+| `--brand-soft` | `#2d0a0a`  | brand-tinted surface (chips, hover washes)                  |
+| `--brand-ink`  | `#fca5a5`  | brand-tinted text (9.0:1 on `--surface`)                    |
+
+The **semantic families are deliberately NOT identity** — do not
+override them: `--accent-*` (deflection amber), `--ok-*` (success
+green), `--err-*` (error red) encode *states*, and they are already AA
+in the built-in theme. A theme that keeps them stays honest: your
+indigo app still tells success from error.
+
+## Rules
+
+- **Filename:** `^[a-z0-9_-]+\.css$` — lowercase, bare filename, in this
+  directory. The server validator rejects anything else at startup
+  (naming the value), so keep the env var and the filename in lockstep.
+- **One `:root` block.** No selectors, no `@media`, no other
+  declarations — the file overrides variables and nothing else (the
+  cascade does the rest). `indigo.css` is the reference shape.
+- **Every text/background pair ≥ 4.5:1** (AGENTS.md rule 5, WCAG 2.1
+  AA). The pairs that matter: `--ink` on `--bg` and on `--surface`,
+  `--ink-soft` on `--surface`, `--bg` on `--brand` (the text on brand
+  buttons is the DARK background ink — that is the pattern), and
+  `--brand-ink` on `--surface`.
+- **Never white-on-brand.** The built-in documents the trap: white on
+  `#f43f5e` is 3.7:1 — it fails. Pick a `--brand` whose luminance
+  carries the dark `--bg` ink at ≥ 4.5:1 (indigo.css: 6.5:1).
+- Keep `--line` close to `--surface` (a 1px step, not a wall) — the
+  layout reads by surfaces, not borders.
+
+## Deployment
+
+- **Dev:** works immediately — the file is served from the static dir
+  (`frontend/`, `BOR_STATIC_DIR`), so drop the file in, set
+  `BOR_THEME`, restart uvicorn.
+- **Container:** rebuild the image. Stage 1 ships the WHOLE directory
+  (`cp -r ./assets/themes /out/assets/themes` — no per-file esbuild), so
+  a new or edited theme file needs **no Containerfile change** (A7):
+  whatever is in `frontend/assets/themes/` at build time is what the
+  image serves at `/assets/themes/…`.
diff --git a/frontend/assets/themes/indigo.css b/frontend/assets/themes/indigo.css
new file mode 100644
index 0000000..a4ae752
--- /dev/null
+++ b/frontend/assets/themes/indigo.css
@@ -0,0 +1,17 @@
+/* Phase 62 example theme — dark indigo/slate.
+   Overrides the :root identity palette from styles.css; every
+   text/background pair meets WCAG 2.1 AA (>= 4.5:1):
+   ink on bg 15.8:1 · ink on surface 14.7:1 · ink-soft on surface 8.3:1
+   dark bg ink on brand 6.5:1 · brand-ink on surface 12.0:1.
+   Semantic families (accent/ok/err) inherit the built-in theme.
+   Load with BOR_THEME=indigo.css (authoring guide: themes/README.md). */
+:root {
+  --bg: #0a0e1a;
+  --surface: #111726;
+  --ink: #e6e9f0;
+  --ink-soft: #a8b0c8;
+  --line: #232c44;
+  --brand: #818cf8;
+  --brand-soft: #1a1f38;
+  --brand-ink: #c7d2fe;
+}
diff --git a/tests/conftest.py b/tests/conftest.py
index 7216087..7f22eb4 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -38,6 +38,15 @@ from app.config import Settings as _Settings  # noqa: E402
 os.environ["BOR_DOCS_REPO"] = ""
 os.environ["BOR_SUGGESTIONS"] = json.dumps(_Settings.model_fields["suggestions"].default)
 
+# Phase 62: the same leak class for the new UI customization settings —
+# an operator's local ``.env`` may legitimately carry
+# ``BOR_INPUT_PLACEHOLDER`` / ``BOR_FOOTER_TEXT`` / ``BOR_THEME``, and
+# the default-metadata pins must see the code defaults (derived from
+# the class fields, same pattern as the suggestions line above).
+os.environ["BOR_INPUT_PLACEHOLDER"] = _Settings.model_fields["input_placeholder"].default
+os.environ["BOR_FOOTER_TEXT"] = _Settings.model_fields["footer_text"].default
+os.environ["BOR_THEME"] = _Settings.model_fields["theme"].default
+
 from app.db import SessionLocal, db_available  # noqa: E402
 from app.main import app as fastapi_app  # noqa: E402
 
diff --git a/tests/e2e/conftest.py b/tests/e2e/conftest.py
index e088c90..788c6e5 100644
--- a/tests/e2e/conftest.py
+++ b/tests/e2e/conftest.py
@@ -112,6 +112,16 @@ def app_server(mock_llm: int) -> Iterator[str]:
     env["BOR_SUGGESTIONS"] = json.dumps(
         _Settings.model_fields["suggestions"].default
     )
+    # Phase 62: the same leak class for the new UI customization
+    # settings — an operator's local (gitignored) ``.env`` may
+    # legitimately carry ``BOR_INPUT_PLACEHOLDER`` / ``BOR_FOOTER_TEXT``
+    # / ``BOR_THEME``, and the byte-identical default contract (task
+    # 05's ``test_default_server_is_byte_identical``) must see the code
+    # defaults (derived from the class fields, never drifts from
+    # ``app/config.py``).
+    env["BOR_INPUT_PLACEHOLDER"] = _Settings.model_fields["input_placeholder"].default
+    env["BOR_FOOTER_TEXT"] = _Settings.model_fields["footer_text"].default
+    env["BOR_THEME"] = _Settings.model_fields["theme"].default
     proc = subprocess.Popen(
         [sys.executable, "-m", "uvicorn", "app.main:app",
          "--host", "127.0.0.1", "--port", str(APP_PORT), "--log-level", "warning"],
diff --git a/tests/e2e/test_configurable_brand.py b/tests/e2e/test_configurable_brand.py
index aab4da3..26cc40a 100644
--- a/tests/e2e/test_configurable_brand.py
+++ b/tests/e2e/test_configurable_brand.py
@@ -146,16 +146,28 @@ def test_api_config_serves_both_names(testy_server: str, app_server: str) -> Non
     body = r.json()
     # Phase 59 (task 05): the third key is the docs-push flag — the
     # "Save as doc" gating; both instances run with BOR_DOCS_REPO
-    # empty, so it is the inert false here.
-    assert set(body) == {"app_name", "version", "docs_repo_configured"}
+    # empty, so it is the inert false here. Phase 62 (task 01): the
+    # endpoint grew to six keys — this suite's instances carry no
+    # UI-customization overrides, so the three new keys are their
+    # defaults.
+    assert set(body) == {
+        "app_name", "version", "docs_repo_configured",
+        "input_placeholder", "footer_text", "theme",
+    }
     assert body["app_name"] == TESTY_NAME
     assert body["docs_repo_configured"] is False
 
     # The shared conftest instance keeps the default (the other
-    # suites' title/label contract rides on it).
+    # suites' title/label contract rides on it) — and its key set
+    # grew with the endpoint (phase 62).
     r2 = httpx.get(f"{app_server}/api/config", timeout=5)
     assert r2.status_code == 200
-    assert r2.json()["app_name"] == DEFAULT_NAME
+    r2_body = r2.json()
+    assert set(r2_body) == {
+        "app_name", "version", "docs_repo_configured",
+        "input_placeholder", "footer_text", "theme",
+    }
+    assert r2_body["app_name"] == DEFAULT_NAME
 
 
 # ---------------------------------------------------------------------------
diff --git a/tests/e2e/test_ui_customization.py b/tests/e2e/test_ui_customization.py
new file mode 100644
index 0000000..dca44e2
--- /dev/null
+++ b/tests/e2e/test_ui_customization.py
@@ -0,0 +1,331 @@
+"""Phase 62 E2E (Playwright): UI customization — placeholder, footer, theme.
+
+Source: ``TODO.md`` L3 — "Allow UI customization. This is brain of reese,
+but I want anyone to be able to deploy it with their name… custom
+message-input placeholder, custom footer-inner text, custom color
+themes…" (owner-locked 2026-09-01: ``BOR_INPUT_PLACEHOLDER``,
+``BOR_FOOTER_TEXT``, ``BOR_THEME`` — A4/A5).
+Run in isolation (DB must be up: ``podman compose up -d db``):
+
+    uv run pytest tests/e2e/test_ui_customization.py -v --no-cov
+
+Contract under test:
+
+* an instance booted with ALL THREE customization vars set shows the
+  custom look end-to-end: the ``GET /api/config`` overrides, the chat
+  composer placeholder (``#message-input``), the footer line on multiple
+  pages (``.footer-text``), and the computed ``:root --brand`` from the
+  inserted ``<link id="theme-override" href="/assets/themes/indigo.css">``
+  (the indigo example theme, ``--brand: #818cf8``);
+* with NOTHING set the shared conftest server is byte-identical to the
+  phase-39/61 no-op contract: the default placeholder, the default
+  footer, NO theme link, the built-in ``--brand: #f43f5e``;
+* a malformed ``BOR_THEME`` (``../evil.css``) refuses startup loudly,
+  naming the value — the phase-56 fail-loud style, proven end-to-end
+  via a real boot attempt, not just the validator unit test.
+
+Determinism note: this story needs a SECOND app instance — the shared
+conftest server keeps the defaults (every other suite's
+placeholder/footer/palette assertions depend on it), so ``custom_server``
+boots the same env block the phase-39 brand suite's ``testy_server``
+boots (same DB, the mock-LLM base URL, the admin auth, the static dir,
+the mock-calibrated threshold) with exactly three changes: port
+``APP_PORT + 2`` (the brand suite owns ``APP_PORT + 1`` — do not
+collide) and the three env overrides. Every assertion is settled-state:
+Playwright's ``expect`` retries ride out the brand.js ``/api/config``
+fetch (the three keys are applied asynchronously, in the SAME fetch's
+settled ``.then`` — no second network call). The one absence assertion
+(no ``#theme-override`` on the default server) first waits for
+``window.BOR_CONFIG_PROMISE`` to settle, so it cannot race the fetch.
+
+Test → contract mapping (Playwright Mapping Rule):
+1. ``test_config_serves_the_overrides``
+2. ``test_chat_page_shows_custom_placeholder_footer_theme``
+3. ``test_footer_text_applies_on_other_pages``
+4. ``test_default_server_is_byte_identical``
+5. ``test_malformed_theme_refuses_startup``
+"""
+from __future__ import annotations
+
+import os
+import subprocess
+import sys
+from collections.abc import Iterator
+
+import httpx
+import pytest
+from playwright.sync_api import Page, expect
+
+from e2e.conftest import (
+    ADMIN_PASSWORD,
+    APP_PORT,
+    REPO,
+    SESSION_SECRET,
+    USE_REAL_LLM,
+    _wait_http,
+)
+
+CUSTOM_PORT = APP_PORT + 2  # the brand suite owns APP_PORT + 1 — no collision
+CUSTOM_URL = f"http://127.0.0.1:{CUSTOM_PORT}"
+MALFORMED_PORT = APP_PORT + 3  # the refused boot never starts listening
+
+# The three overrides (task 05) — the whole story:
+CUSTOM_PLACEHOLDER = "Ask the archive…"
+CUSTOM_FOOTER = "Custom footer line"
+CUSTOM_THEME = "indigo.css"
+INDIGO_BRAND = "#818cf8"  # indigo.css's --brand (the computed token)
+
+# The phase-39/61 no-op contract on the shared default server:
+DEFAULT_NAME = "Brain of Reese"
+DEFAULT_PLACEHOLDER = "Ask me anything…"
+DEFAULT_FOOTER = "Powered by self-hosted models"
+BUILTIN_BRAND = "#f43f5e"  # styles.css's built-in --brand
+
+
+@pytest.fixture(scope="session")
+def custom_server(mock_llm: int) -> Iterator[str]:
+    """A SECOND app instance, booted with all three customization
+    overrides.
+
+    The shared conftest ``app_server`` keeps the defaults (every other
+    suite's placeholder/footer/palette assertions depend on it) — so
+    this fixture copies the phase-39 brand suite's ``testy_server`` env
+    block verbatim (same DB, the mock-LLM base URL,
+    ``BOR_ADMIN_PASSWORD``/``BOR_SESSION_SECRET``, ``BOR_STATIC_DIR``,
+    ``BOR_RELEVANCE_THRESHOLD``) with exactly three changes: port
+    ``APP_PORT + 2`` (the brand suite owns ``APP_PORT + 1``) and the
+    three env overrides below. Started after ``mock_llm`` is available
+    (its fixture dependency).
+    """
+    env = dict(os.environ)
+    env.pop("DEBUGPY", None)
+    env["BOR_ENVIRONMENT"] = "e2e"
+    env["BOR_STATIC_DIR"] = str(REPO / "frontend")
+    env["BOR_LLM_BASE_URL"] = (
+        "https://aipi.reeseapps.com/v1"
+        if USE_REAL_LLM
+        else f"http://127.0.0.1:{mock_llm}/v1"
+    )
+    # The mock's token-overlap embeddings have their own score
+    # distribution — the same mock-calibrated threshold as the shared
+    # instance, so this suite's pages behave like every other story's.
+    env["BOR_RELEVANCE_THRESHOLD"] = "0.30"
+    env.setdefault(
+        "BOR_DATABASE_URL",
+        "postgresql+psycopg://reese:reese@localhost:5432/brain_of_reese",
+    )
+    # Phase 16: admin auth must be set or create_app() refuses to boot.
+    env["BOR_ADMIN_PASSWORD"] = ADMIN_PASSWORD
+    env["BOR_SESSION_SECRET"] = SESSION_SECRET
+    # Phase 62 (owner-locked 2026-09-01, TODO L3) — the whole story:
+    env["BOR_INPUT_PLACEHOLDER"] = CUSTOM_PLACEHOLDER
+    env["BOR_FOOTER_TEXT"] = CUSTOM_FOOTER
+    env["BOR_THEME"] = CUSTOM_THEME
+    proc = subprocess.Popen(
+        [sys.executable, "-m", "uvicorn", "app.main:app",
+         "--host", "127.0.0.1", "--port", str(CUSTOM_PORT), "--log-level", "warning"],
+        cwd=REPO,
+        env=env,
+    )
+    try:
+        _wait_http(f"{CUSTOM_URL}/api/health")
+        yield CUSTOM_URL
+    finally:
+        proc.terminate()
+        try:
+            proc.wait(timeout=10)
+        except subprocess.TimeoutExpired:
+            proc.kill()
+
+
+def wait_for_brand_settled(page: Page, timeout: int = 15_000) -> None:
+    """Wait for the brand layer's boot fetch to settle.
+
+    The three customization keys are applied asynchronously, in the
+    settled ``/api/config`` promise's ``.then`` — absence assertions
+    (no ``#theme-override``) must not race that fetch. The promise
+    NEVER rejects (the brand.js contract), so its resolution means the
+    DOM pass has already run: ``applyBrand`` registered its callback on
+    the same promise at page load, before this wait's callback, and
+    promise callbacks run in registration order."""
+    page.wait_for_function(
+        "() => window.BOR_CONFIG_PROMISE.then(() => true)",
+        timeout=timeout,
+    )
+
+
+def expect_brand_var(page: Page, expected: str, timeout: int = 15_000) -> None:
+    """Retrying computed ``:root --brand`` equality. Custom properties
+    return the SPECIFIED token from ``getComputedStyle`` (no color
+    normalization), so the string compare is stable: ``#818cf8`` is
+    exactly what indigo.css declares, ``#f43f5e`` exactly what
+    styles.css declares (the built-in)."""
+    page.wait_for_function(
+        """(expected) =>
+            getComputedStyle(document.documentElement)
+                .getPropertyValue("--brand")
+                .trim() === expected""",
+        arg=expected,
+        timeout=timeout,
+    )
+
+
+# ---------------------------------------------------------------------------
+# 1. The endpoint the brand layer reads — the three overrides, the
+#    six-key set, and the theme file served from the dev static dir
+# ---------------------------------------------------------------------------
+
+
+def test_config_serves_the_overrides(custom_server: str) -> None:
+    r = httpx.get(f"{CUSTOM_URL}/api/config", timeout=5)
+    assert r.status_code == 200
+    body = r.json()
+    # The six-key set (the phase-39/59/62 endpoint contract) with the
+    # three customization overrides — the app NAME stays the default
+    # (this suite does not re-test BOR_APP_NAME; that is the phase-39
+    # suite's job).
+    assert set(body) == {
+        "app_name", "version", "docs_repo_configured",
+        "input_placeholder", "footer_text", "theme",
+    }
+    assert body["app_name"] == DEFAULT_NAME
+    assert body["input_placeholder"] == CUSTOM_PLACEHOLDER
+    assert body["footer_text"] == CUSTOM_FOOTER
+    assert body["theme"] == CUSTOM_THEME
+
+    # Served in dev from the static dir (the no-CDN rule): the theme
+    # file the boot fetch names is reachable at its served path, and
+    # it is the indigo example (its --brand is the E2E's theme proof).
+    r2 = httpx.get(f"{CUSTOM_URL}/assets/themes/{CUSTOM_THEME}", timeout=5)
+    assert r2.status_code == 200
+    assert f"--brand: {INDIGO_BRAND}" in r2.text
+
+
+# ---------------------------------------------------------------------------
+# 2. The chat page — placeholder, footer, the theme link + effect
+# ---------------------------------------------------------------------------
+
+
+def test_chat_page_shows_custom_placeholder_footer_theme(
+    page: Page, custom_server: str
+) -> None:
+    page.goto(custom_server + "/")
+    # 5. The composer placeholder — the retry rides out the brand.js
+    #    /api/config fetch that applies it.
+    expect(page.locator("#message-input")).to_have_attribute(
+        "placeholder", CUSTOM_PLACEHOLDER, timeout=15_000
+    )
+    # 6. The footer line on the chat page.
+    expect(page.locator(".footer-text").first).to_have_text(
+        CUSTOM_FOOTER, timeout=15_000
+    )
+    # 7. The theme link in <head> — rel=stylesheet, the served path.
+    expect(page.locator('head link#theme-override[rel="stylesheet"]')).to_have_attribute(
+        "href", f"/assets/themes/{CUSTOM_THEME}", timeout=15_000
+    )
+    # And it takes effect: the computed :root --brand is the indigo
+    # value (the built-in #f43f5e means the theme never loaded).
+    expect_brand_var(page, INDIGO_BRAND)
+
+
+# ---------------------------------------------------------------------------
+# 3. A second page — the footer applies multi-page; the placeholder
+#    application no-ops without a composer
+# ---------------------------------------------------------------------------
+
+
+def test_footer_text_applies_on_other_pages(page: Page, custom_server: str) -> None:
+    page.goto(custom_server + "/login.html")
+    # This page has NO composer — the placeholder application no-ops
+    # there via the null guard (no error, no element touched).
+    expect(page.locator("#message-input")).to_have_count(0)
+    # The footer line applies on every page (the phase-61 hook).
+    expect(page.locator(".footer-text").first).to_have_text(
+        CUSTOM_FOOTER, timeout=15_000
+    )
+    # The theme link rides in <head> on every page too.
+    expect(page.locator('head link#theme-override[rel="stylesheet"]')).to_have_attribute(
+        "href", f"/assets/themes/{CUSTOM_THEME}", timeout=15_000
+    )
+
+
+# ---------------------------------------------------------------------------
+# 4. The no-op regression — the shared default server is byte-identical
+#    to the phase-39/61 contract
+# ---------------------------------------------------------------------------
+
+
+def test_default_server_is_byte_identical(page: Page, app_server: str) -> None:
+    page.goto(app_server + "/")
+    # Settle the boot fetch BEFORE the absence assertion — it must not
+    # race the (absent) theme-link insertion.
+    wait_for_brand_settled(page)
+    # The phase-39/61 no-op contract: the template defaults stand.
+    expect(page.locator("#message-input")).to_have_attribute(
+        "placeholder", DEFAULT_PLACEHOLDER
+    )
+    expect(page.locator(".footer-text").first).to_have_text(DEFAULT_FOOTER)
+    # With BOR_THEME unset the brand layer inserts NO theme link:
+    assert page.locator("#theme-override").count() == 0, (
+        "with BOR_THEME unset the brand layer must NOT insert a theme "
+        "link (the byte-identical no-op contract)"
+    )
+    # The built-in dark-tech palette stands.
+    expect_brand_var(page, BUILTIN_BRAND)
+
+
+# ---------------------------------------------------------------------------
+# 5. The fail-loud boot check — a malformed BOR_THEME refuses startup
+# ---------------------------------------------------------------------------
+
+
+def test_malformed_theme_refuses_startup() -> None:
+    """A malformed ``BOR_THEME`` (``../evil.css`` — a path, exactly the
+    shape the A5 lock names as illegal) kills startup with the value
+    NAMED on stderr (the phase-56 fail-loud house style), proven
+    end-to-end via a real uvicorn boot attempt: the process exits
+    non-zero within the timeout without ever starting to listen.
+
+    ``app.main`` builds its settings at import time
+    (``settings = get_settings()``), so the validator fires during the
+    ASGI app import — before admin auth, before the port binds."""
+    env = dict(os.environ)
+    env.pop("DEBUGPY", None)
+    env["BOR_ENVIRONMENT"] = "e2e"
+    env["BOR_STATIC_DIR"] = str(REPO / "frontend")
+    env["BOR_RELEVANCE_THRESHOLD"] = "0.30"
+    env.setdefault(
+        "BOR_DATABASE_URL",
+        "postgresql+psycopg://reese:reese@localhost:5432/brain_of_reese",
+    )
+    env["BOR_ADMIN_PASSWORD"] = ADMIN_PASSWORD
+    env["BOR_SESSION_SECRET"] = SESSION_SECRET
+    # The whole point: a malformed theme value.
+    env["BOR_THEME"] = "../evil.css"
+    proc = subprocess.Popen(
+        [sys.executable, "-m", "uvicorn", "app.main:app",
+         "--host", "127.0.0.1", "--port", str(MALFORMED_PORT), "--log-level", "warning"],
+        cwd=REPO,
+        env=env,
+        stdout=subprocess.DEVNULL,
+        stderr=subprocess.PIPE,
+        text=True,
+    )
+    try:
+        proc.wait(timeout=60)
+    except subprocess.TimeoutExpired:
+        proc.kill()
+        proc.wait()
+        pytest.fail(
+            "the app kept running with BOR_THEME='../evil.css' — a "
+            "malformed theme must refuse startup, not silently 404"
+        )
+    assert proc.returncode != 0, (
+        "the malformed BOR_THEME must make uvicorn exit non-zero"
+    )
+    stderr = proc.stderr.read() if proc.stderr else ""
+    # Fail-loud names the offending value (phase-56 house style):
+    assert "'../evil.css'" in stderr, (
+        f"stderr must name the offending value, got tail: {stderr[-2000:]}"
+    )
+    assert "theme must be a bare .css filename" in stderr
diff --git a/tests/integration/test_api.py b/tests/integration/test_api.py
index 7526a29..19ab7eb 100644
--- a/tests/integration/test_api.py
+++ b/tests/integration/test_api.py
@@ -18,16 +18,26 @@ def test_health_reports_ok(client) -> None:
 
 
 def test_config_returns_default_app_metadata(client) -> None:
-    """GET /api/config is public (anonymous) and returns exactly three
-    keys — the phase-39 app metadata + the phase-59 docs flag (inert
-    false while BOR_DOCS_REPO is empty — the "Save as doc" gating)."""
+    """GET /api/config is public (anonymous) and returns exactly six
+    keys — the phase-39 app metadata, the phase-59 docs flag (inert
+    false while BOR_DOCS_REPO is empty — the "Save as doc" gating),
+    and the phase-62 UI customization strings (composer placeholder,
+    footer line, theme file name)."""
     r = client.get("/api/config")
     assert r.status_code == 200
     body = r.json()
-    assert set(body) == {"app_name", "version", "docs_repo_configured"}
+    assert set(body) == {
+        "app_name", "version", "docs_repo_configured",
+        "input_placeholder", "footer_text", "theme",
+    }
     assert body["app_name"] == "Brain of Reese"
     assert body["version"] == get_settings().app_version
     assert body["docs_repo_configured"] is False
+    # Phase 62: UNSET => the phase-61 neutral copy stands (the
+    # byte-identical contract); an empty theme = the built-in palette.
+    assert body["input_placeholder"] == "Ask me anything…"
+    assert body["footer_text"] == "Powered by self-hosted models"
+    assert body["theme"] == ""
 
 
 def test_config_follows_overridden_app_name(client) -> None:
@@ -42,7 +52,10 @@ def test_config_follows_overridden_app_name(client) -> None:
         r = client.get("/api/config")
         assert r.status_code == 200
         body = r.json()
-        assert set(body) == {"app_name", "version", "docs_repo_configured"}
+        assert set(body) == {
+            "app_name", "version", "docs_repo_configured",
+            "input_placeholder", "footer_text", "theme",
+        }
         assert body["app_name"] == "Brain of Testy"
         assert body["version"] == "0.1.0"
         assert body["docs_repo_configured"] is False
@@ -50,6 +63,34 @@ def test_config_follows_overridden_app_name(client) -> None:
         fastapi_app.dependency_overrides.clear()
 
 
+def test_config_serves_ui_customization_overrides(client) -> None:
+    """Phase 62: the three UI customization keys mirror Settings
+    overrides (``BOR_INPUT_PLACEHOLDER`` / ``BOR_FOOTER_TEXT`` /
+    ``BOR_THEME``) verbatim — the values the frontend brand layer
+    applies at boot, so this dict is the whole contract."""
+    from app.config import Settings
+    from app.main import app as fastapi_app
+
+    fastapi_app.dependency_overrides[get_settings] = lambda: Settings(
+        input_placeholder="Ask the vault…",
+        footer_text="Powered by my own models",
+        theme="indigo.css",
+    )
+    try:
+        r = client.get("/api/config")
+        assert r.status_code == 200
+        body = r.json()
+        assert set(body) == {
+            "app_name", "version", "docs_repo_configured",
+            "input_placeholder", "footer_text", "theme",
+        }
+        assert body["input_placeholder"] == "Ask the vault…"
+        assert body["footer_text"] == "Powered by my own models"
+        assert body["theme"] == "indigo.css"
+    finally:
+        fastapi_app.dependency_overrides.clear()
+
+
 def test_config_docs_flag_tracks_settings(client) -> None:
     """Phase 59 (task 05): ``docs_repo_configured`` mirrors
     ``settings.docs_configured`` — a real bool (never a truthy string)
diff --git a/tests/unit/test_config.py b/tests/unit/test_config.py
index d20b7ef..3e9bca1 100644
--- a/tests/unit/test_config.py
+++ b/tests/unit/test_config.py
@@ -397,3 +397,77 @@ def test_docs_branchs_garbage_ignored_when_repo_unset(
     s = _settings()
     assert s.docs_configured is False
     assert s.docs_branch == "bor docs.."  # stored verbatim, never used
+
+
+# --- UI customization (phase 62, TODO L3) ---
+
+
+def test_ui_customization_defaults_are_the_phase_61_copy() -> None:
+    """UNSET => byte-identical to the phase-61 neutral UI: the locked
+    phase-61 copy is the DEFAULT (composer placeholder + footer line),
+    and an empty theme = the built-in dark-tech palette."""
+    s = _settings()
+    assert s.input_placeholder == "Ask me anything…"
+    assert s.footer_text == "Powered by self-hosted models"
+    assert s.theme == ""
+
+
+def test_ui_customization_env_overrides(monkeypatch: pytest.MonkeyPatch) -> None:
+    """The three settings honor their ``BOR_`` env vars
+    (``BOR_INPUT_PLACEHOLDER`` / ``BOR_FOOTER_TEXT`` / ``BOR_THEME``);
+    placeholder/footer accept any string (empty is legal — the brand
+    layer then keeps the template default)."""
+    monkeypatch.setenv("BOR_INPUT_PLACEHOLDER", "Ask the vault…")
+    monkeypatch.setenv("BOR_FOOTER_TEXT", "Powered by my own models")
+    monkeypatch.setenv("BOR_THEME", "indigo.css")
+    s = _settings()
+    assert s.input_placeholder == "Ask the vault…"
+    assert s.footer_text == "Powered by my own models"
+    assert s.theme == "indigo.css"
+    monkeypatch.setenv("BOR_INPUT_PLACEHOLDER", "")
+    assert _settings().input_placeholder == ""  # empty stands
+
+
+def test_theme_validator_accepts_empty_and_bare_css_filename() -> None:
+    """Phase 62 (A5): empty = the built-in palette; a bare lowercase
+    ``.css`` filename (the ``indigo.css`` example) is the only
+    non-empty shape — dashes/underscores/digits are legal tokens."""
+    assert _settings().theme == ""  # "" passes
+    assert _settings(theme="indigo.css").theme == "indigo.css"
+    assert _settings(theme="dark-2026_v2.css").theme == "dark-2026_v2.css"
+
+
+@pytest.mark.parametrize(
+    ("bad", "match"),
+    [
+        # uppercase — the shape is lowercase-only
+        ("Indigo.css", "Indigo.css"),
+        # path escape — a theme is a filename, never a path
+        ("../evil.css", r"\.\./evil\.css"),
+        ("a/b.css", r"a/b\.css"),
+        ("/abs.css", r"got '/abs\.css'"),
+        # a missing extension is not a theme file
+        ("indigo", r"got 'indigo'"),  # must not match the example text
+    ],
+)
+def test_theme_validator_rejects_malformed_naming_the_value(
+    bad: str,
+    match: str,
+) -> None:
+    """A typo in ``BOR_THEME`` must kill startup, not silently 404 at
+    runtime — the rejection names the offending value (the phase-56
+    fail-loud house style) alongside the allowed shape."""
+    with pytest.raises(ValidationError, match=match):
+        _settings(theme=bad)
+
+
+def test_bor_theme_env_malformed_fails_startup_naming_value(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """The startup path: a malformed ``BOR_THEME`` in the environment
+    fails Settings construction loudly (the app builds its settings at
+    import time, so this is a refused boot), naming the value — the
+    E2E boots-check lands in task 05."""
+    monkeypatch.setenv("BOR_THEME", "../evil.css")
+    with pytest.raises(ValidationError, match=r"\.\./evil\.css"):
+        _settings()
diff --git a/tests/unit/test_frontend_brand.py b/tests/unit/test_frontend_brand.py
index 2d40c59..9c8d992 100644
--- a/tests/unit/test_frontend_brand.py
+++ b/tests/unit/test_frontend_brand.py
@@ -95,6 +95,60 @@ def test_brand_js_reskins_title_brand_text_prose_and_attributes() -> None:
         assert marker in js, f"the attribute pass must cover {marker}"
 
 
+def test_brand_js_applies_phase_62_customization_from_the_same_fetch() -> None:
+    """Phase 62 (owner-locked 2026-09-01, TODO L3): the SAME settled
+    /api/config answer also drives the three customization keys — the
+    #message-input placeholder, every .footer-text node, and the theme
+    stylesheet link (inserted right after the styles.css link, guarded
+    by #theme-override, degrading with a console.warn on 404 — A5).
+    No second network call: the keys ride the existing boot fetch."""
+    js = _text(BRAND_JS)
+    assert js.count('= fetch("/api/config"') == 1, (
+        "the three keys must ride the existing boot fetch — no new call"
+    )
+    # 5. The composer placeholder (chat page only — the null guard
+    #    no-ops on every other page).
+    assert 'document.querySelector("#message-input")' in js
+    assert "input_placeholder" in js
+    # 6. The footer line on all 9 pages (the phase-61 hook) — via
+    #    textContent: an operator string can't inject markup.
+    assert 'document.querySelectorAll(".footer-text")' in js
+    assert "footer_text" in js
+    # 7. The theme link: /assets/themes/<name>, inserted right after
+    #    the styles.css link, tagged #theme-override (the idempotency
+    #    guard), with the A5 degradation warn.
+    assert '"/assets/themes/"' in js
+    assert 'link.id = "theme-override"' in js
+    assert 'getElementById("theme-override")' in js
+    assert 'insertAdjacentElement("afterend", link)' in js
+    assert "link.onerror" in js
+    assert '"brand: theme " + themeName' in js
+    # The styles.css finder must survive the phase-33/54 cache-bust
+    # rewrite: the SERVED HTML carries the asset ref with a
+    # ?v=<token> query (and el.href is the absolute URL), so the match
+    # has to run on the RAW attribute path with query/fragment
+    # stripped — el.href.endsWith(…) would silently skip the insertion
+    # (the theme never applied; found by the task-05 E2E).
+    assert 'getAttribute("href")' in js
+    assert "split(/[?#]/)[0]" in js
+    assert 'endsWith("styles.css")' in js
+    assert "el.href.endsWith" not in js
+    # The empty-skip no-op contract: each key is guarded before any
+    # DOM write, so an unset deployment stays byte-identical.
+    for guard in ("if (placeholder) {", "if (footerText) {", "if (themeName) {"):
+        assert guard in js, (
+            f"an empty value must skip its application ({guard})"
+        )
+    # Independence: the phase-62 block sits AFTER the app_name passes
+    # in the same .then — never gated by the name.
+    assert js.index("// 4. Attributes:") < js.index("// Phase 62"), (
+        "the customization keys must apply after the app_name block, "
+        "even when the name is the default/empty"
+    )
+    # The app_name literal default pin still holds.
+    assert 'window.BOR_BRAND = "Brain of Reese"' in js
+
+
 def test_page_scripts_keep_the_default_literal_exactly_once() -> None:
     """The fallback literal lives in the page scripts' brand() reads —
     exactly one copy per file (a second copy could drift out of sync)."""
diff --git a/tests/unit/test_save_as_doc_button.py b/tests/unit/test_save_as_doc_button.py
index 6f694f2..0e035fa 100644
--- a/tests/unit/test_save_as_doc_button.py
+++ b/tests/unit/test_save_as_doc_button.py
@@ -51,7 +51,12 @@ def test_app_config_dict_carries_the_docs_flag() -> None:
 
     s = _settings()
     body = app_config(s)
-    assert set(body) == {"app_name", "version", "docs_repo_configured"}
+    # Phase 62 (task 01): the response grew to the six-key set — the
+    # phase-62 UI customization keys ride the SAME endpoint.
+    assert set(body) == {
+        "app_name", "version", "docs_repo_configured",
+        "input_placeholder", "footer_text", "theme",
+    }
     assert body["docs_repo_configured"] is s.docs_configured
     assert body["docs_repo_configured"] is False
 
diff --git a/tests/unit/test_themes.py b/tests/unit/test_themes.py
new file mode 100644
index 0000000..078c805
--- /dev/null
+++ b/tests/unit/test_themes.py
@@ -0,0 +1,195 @@
+"""Unit: the phase-62 example theme (``frontend/assets/themes/``) and
+the Containerfile line that ships it (A7).
+
+No Python logic exists for this task — the mechanism lives in
+``brand.js`` (pinned by test_frontend_brand.py) and the theme is a
+drop-in stylesheet. Like the other frontend-adjacent unit files, this
+module pins the assets as text, so a silent regression (a theme file
+gaining a selector, a declaration drifting, the Containerfile line
+vanishing) is caught without a browser. The browser-visible layer
+(computed ``--brand``, the inserted ``<link>``) is E2E-gated by
+``tests/e2e/test_ui_customization.py`` (task 05).
+"""
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[2]
+FRONTEND = REPO_ROOT / "frontend"
+THEMES = FRONTEND / "assets" / "themes"
+INDIGO = THEMES / "indigo.css"
+GUIDE = THEMES / "README.md"
+CONTAINERFILE = REPO_ROOT / "Containerfile"
+
+#: The 8 identity variables a theme may override — and the EXACT set
+#: indigo.css ships (the semantic families accent/ok/err are states,
+#: not identity: a theme that overrides them stops being honest).
+IDENTITY_VARS = (
+    "--bg",
+    "--surface",
+    "--ink",
+    "--ink-soft",
+    "--line",
+    "--brand",
+    "--brand-soft",
+    "--brand-ink",
+)
+
+INDIGO_VALUES: dict[str, str] = {
+    "--bg": "#0a0e1a",
+    "--surface": "#111726",
+    "--ink": "#e6e9f0",
+    "--ink-soft": "#a8b0c8",
+    "--line": "#232c44",
+    "--brand": "#818cf8",
+    "--brand-soft": "#1a1f38",
+    "--brand-ink": "#c7d2fe",
+}
+
+
+def _text(path: Path) -> str:
+    return path.read_text(encoding="utf-8")
+
+
+def _strip_comments(css: str) -> str:
+    """Drop ``/* … */`` comments — the pins assert against declarations,
+    not prose."""
+    return re.sub(r"/\*.*?\*/", "", css, flags=re.S)
+
+
+def _declarations(css: str) -> dict[str, str]:
+    """The ``--name: value`` declarations of the (single) ``:root``
+    block, in file order."""
+    return dict(re.findall(r"(--[a-z-]+)\s*:\s*([^;]+);", css))
+
+
+def test_example_theme_files_exist() -> None:
+    """The example theme and its authoring guide ship in the static
+    dir (served at /assets/themes/… in dev AND in the image)."""
+    assert INDIGO.is_file(), f"missing example theme: {INDIGO}"
+    assert GUIDE.is_file(), f"missing authoring guide: {GUIDE}"
+
+
+def test_indigo_starts_with_a_single_root_block_and_nothing_else() -> None:
+    """The whole file is ONE ``:root`` block (the cascade is the entire
+    mechanism): after stripping comments the first non-whitespace
+    content is ``:root``, and no other rule, selector, or declaration
+    exists anywhere in the file."""
+    css = _strip_comments(_text(INDIGO))
+    assert css.lstrip().startswith(":root"), (
+        "indigo.css must start with the :root block (after its header "
+        "comment) — nothing may precede it"
+    )
+    assert re.fullmatch(r"\s*:root\s*\{[^{}]*\}\s*", css, re.S) is not None, (
+        "indigo.css must be exactly one :root block — no selectors, "
+        "no @media, no nested or extra rules"
+    )
+
+
+def test_indigo_overrides_exactly_the_eight_identity_variables() -> None:
+    """EXACTLY the 8 identity overrides with the locked values — no
+    other declarations (a 9th declaration here would be the theme
+    reaching past the palette), and the semantic families
+    (accent/ok/err) must be untouched (they encode states)."""
+    decls = _declarations(_strip_comments(_text(INDIGO)))
+    assert set(decls) == set(IDENTITY_VARS), (
+        f"indigo.css must override exactly the 8 identity variables, got "
+        f"{sorted(decls)}"
+    )
+    for name in IDENTITY_VARS:
+        assert decls[name].strip() == INDIGO_VALUES[name], (
+            f"{name} drifted from the locked value "
+            f"{INDIGO_VALUES[name]!r}, got {decls[name].strip()!r}"
+        )
+    for family in ("--accent-", "--ok-", "--err-"):
+        assert not any(k.startswith(family) for k in decls), (
+            f"semantic {family}* variables must stay the built-in "
+            f"theme (they encode states)"
+        )
+
+
+def test_indigo_identity_pairs_meet_wcag_aa() -> None:
+    """The five identity text/background pairs, computed from the file's
+    OWN hex values (not re-typed), each meet WCAG 2.1 AA (>= 4.5:1) —
+    AGENTS.md rule 5. The pairs are the ones the layout actually pairs:
+    ink on bg/surface, ink-soft on surface, the dark bg ink on brand
+    (text on brand buttons is --bg, never white — the built-in's
+    documented 3.7:1 trap), brand-ink on surface."""
+    decls = _declarations(_strip_comments(_text(INDIGO)))
+
+    def lum(hexcolor: str) -> float:
+        h = hexcolor.lstrip("#")
+        chans = (int(h[i : i + 2], 16) / 255.0 for i in (0, 2, 4))
+        lin = [
+            c / 12.92 if c <= 0.04045 else ((c + 0.055) / 1.055) ** 2.4
+            for c in chans
+        ]
+        r, g, b = lin
+        return 0.2126 * r + 0.7152 * g + 0.0722 * b
+
+    def ratio(fg: str, bg: str) -> float:
+        l1, l2 = lum(fg), lum(bg)
+        return (max(l1, l2) + 0.05) / (min(l1, l2) + 0.05)
+
+    pairs = (
+        ("ink on bg", decls["--ink"], decls["--bg"]),
+        ("ink on surface", decls["--ink"], decls["--surface"]),
+        ("ink-soft on surface", decls["--ink-soft"], decls["--surface"]),
+        ("bg ink on brand", decls["--bg"], decls["--brand"]),
+        ("brand-ink on surface", decls["--brand-ink"], decls["--surface"]),
+    )
+    for name, fg, bg in pairs:
+        r = ratio(fg, bg)
+        assert r >= 4.5, f"{name}: {r:.2f}:1 < 4.5:1 (WCAG 2.1 AA)"
+
+
+def test_containerfile_ships_the_whole_themes_directory() -> None:
+    """A7: stage 1 copies the WHOLE themes directory (no per-file
+    esbuild — a future theme file needs no Containerfile edit), and it
+    does so AFTER the styles.css minify line (so the served /assets/
+    tree is complete before the pages cp)."""
+    cf = _text(CONTAINERFILE)
+    stage1 = cf.split("AS frontend", 1)[1].split("\nFROM", 1)[0]
+    lines = stage1.splitlines()
+    cp_idxs = [
+        i
+        for i, ln in enumerate(lines)
+        if re.search(r"\bcp\s+-r\s+\./assets/themes\s+/out/assets/themes\b", ln)
+    ]
+    assert len(cp_idxs) == 1, (
+        "stage 1 must ship the themes directory with exactly one "
+        "'cp -r ./assets/themes /out/assets/themes' line"
+    )
+    styles_idxs = [
+        i for i, ln in enumerate(lines) if "esbuild ./assets/styles.css" in ln
+    ]
+    assert len(styles_idxs) == 1, "stage 1 must minify styles.css"
+    assert cp_idxs[0] > styles_idxs[0], (
+        "the themes cp must come AFTER the styles.css minify line"
+    )
+    cp_line = lines[cp_idxs[0]]
+    assert "--bundle" not in cp_line and "esbuild" not in cp_line, (
+        "A7: the themes directory is copied verbatim — no per-file "
+        "esbuild minify"
+    )
+
+
+def test_authoring_guide_pins_the_contract() -> None:
+    """The guide documents the load path (BOR_THEME → /api/config →
+    brand.js link after styles.css), the filename validator regex, the
+    8-variable table, the 4.5:1 bar, the never-white-on-brand trap,
+    and the A7 rebuild story (a new file needs no Containerfile edit)."""
+    guide = _text(GUIDE)
+    for marker in (
+        "BOR_THEME",
+        "/api/config",
+        "styles.css",
+        r"^[a-z0-9_-]+\.css$",
+        "4.5:1",
+        "white-on-brand",
+        "cp -r ./assets/themes /out/assets/themes",
+    ):
+        assert marker in guide, f"themes/README.md must document {marker!r}"
+    for var in IDENTITY_VARS:
+        assert var in guide, f"the variable table must list {var}"