diff --git a/CLAUDE.md b/CLAUDE.md
index 945a331..deac08e 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -233,6 +233,9 @@ Presentational config separate from `config.yml`. Controls accent colour, dark/l
 | `nav-link` | `--nav-link-colour` | falls back to `text` |
 | `nav-link-active` | `--nav-link-active-colour` | falls back to `accent` |
 | `nav-section-heading` | `--nav-section-heading-colour` | falls back to `text-muted` |
+| `nav-sitename` | `--nav-sitename-colour` | falls back to `nav-link` |
+| `nav-description` | `--nav-description-colour` | falls back to `nav-section-heading` |
+| `nav-toggle` | `--nav-toggle-colour` | falls back to `nav-section-heading` |
 | `divider` | `--divider` | `color-mix(in srgb, background 85%, text)` |
 
 **When to use nav-link keys:** When `nav-background` matches or is very close to `accent`, the default behaviour (active link coloured with `accent`) makes links invisible. Set `nav-link`, `nav-link-active`, and `nav-section-heading` explicitly so all three are legible against `nav-background`. Example: a red nav background needs white (`#FFFFFF`) for all three nav colour keys.
diff --git a/app/index.html b/app/index.html
index a910816..b0a722b 100644
--- a/app/index.html
+++ b/app/index.html
@@ -59,6 +59,9 @@ if ('serviceWorker' in navigator) {
   --nav-link-colour: var(--nav-font-colour);
   --nav-link-active-colour: var(--accent);
   --nav-section-heading-colour: var(--font-colour-muted);
+  --nav-sitename-colour: var(--nav-link-colour);
+  --nav-description-colour: var(--nav-section-heading-colour);
+  --nav-toggle-colour: var(--nav-section-heading-colour);
   --nav-active-bg: rgba(var(--accent-rgb), 0.10);
   --nav-hover-bg: rgba(var(--accent-rgb), 0.05);
   --font-colour: #1E293B;
@@ -91,6 +94,9 @@ if ('serviceWorker' in navigator) {
   --bg-nav: #1E293B;
   --nav-font-colour: #E2E8F0;
   --nav-link-colour: var(--nav-font-colour);
+  --nav-sitename-colour: var(--nav-link-colour);
+  --nav-description-colour: var(--nav-section-heading-colour);
+  --nav-toggle-colour: var(--nav-section-heading-colour);
   --nav-link-active-colour: var(--accent);
   --nav-section-heading-colour: var(--font-colour-muted);
   --nav-active-bg: rgba(96, 165, 250, 0.15);
@@ -196,14 +202,14 @@ body {
   font-family: var(--font-title);
   font-weight: var(--font-title-weight);
   font-size: 1.15rem;
-  color: var(--nav-link-colour, var(--font-colour));
+  color: var(--nav-sitename-colour);
   line-height: 1.3;
   text-decoration: none;
   display: block;
 }
 .sidebar-sitename:hover { color: var(--nav-link-active-colour, var(--accent)); }
 
-.sidebar-description { font-size: 0.8rem; color: var(--nav-section-heading-colour, var(--font-colour-muted)); margin-top: 0.25rem; line-height: 1.4; }
+.sidebar-description { font-size: 0.8rem; color: var(--nav-description-colour); margin-top: 0.25rem; line-height: 1.4; }
 
 /* Search */
 .search-container { padding: 0.75rem 1.25rem; flex-shrink: 0; }
@@ -341,9 +347,9 @@ body {
   gap: 0.5rem;
   padding: 0.4rem 0.6rem;
   font-size: 0.8rem;
-  color: var(--nav-section-heading-colour, var(--font-colour-muted));
+  color: var(--nav-toggle-colour);
   background: none;
-  border: 1px solid color-mix(in srgb, var(--bg-nav) 70%, var(--nav-link-colour, var(--font-colour)));
+  border: 1px solid color-mix(in srgb, var(--bg-nav) 70%, var(--nav-toggle-colour));
   border-radius: 6px;
   cursor: pointer;
   font-family: var(--font-body);
@@ -351,7 +357,7 @@ body {
   width: 100%;
   justify-content: center;
 }
-.theme-toggle:hover { color: var(--nav-link-colour, var(--font-colour)); border-color: var(--nav-section-heading-colour, var(--font-colour-muted)); }
+.theme-toggle:hover { color: var(--nav-link-colour, var(--font-colour)); border-color: var(--nav-toggle-colour); }
 .theme-toggle svg { width: 16px; height: 16px; flex-shrink: 0; }
 
 /* ═══════════════════════════════════════════
@@ -1259,6 +1265,9 @@ body {
       if (m['nav-link'])            vars.push(`--nav-link-colour: ${m['nav-link']}`);
       if (m['nav-link-active'])     vars.push(`--nav-link-active-colour: ${m['nav-link-active']}`);
       if (m['nav-section-heading']) vars.push(`--nav-section-heading-colour: ${m['nav-section-heading']}`);
+      if (m['nav-sitename'])        vars.push(`--nav-sitename-colour: ${m['nav-sitename']}`);
+      if (m['nav-description'])     vars.push(`--nav-description-colour: ${m['nav-description']}`);
+      if (m['nav-toggle'])          vars.push(`--nav-toggle-colour: ${m['nav-toggle']}`);
       if (m['divider'])             vars.push(`--divider: ${m['divider']}`);
       if (vars.length) modeCss += `:root[data-theme="${mode}"] { ${vars.join('; ')}; }\n`;
     });
diff --git a/app/theme.yml b/app/theme.yml
index e5ff3fe..2fe1838 100644
--- a/app/theme.yml
+++ b/app/theme.yml
@@ -15,6 +15,9 @@ light:
   # nav-link: "#1E293B"          # inactive nav link text (defaults to text)
   # nav-link-active: "#2563EB"   # active nav link text (defaults to accent)
   # nav-section-heading: "#64748B" # nav section label text (defaults to text-muted)
+  # nav-sitename: "#1E293B"      # site name in sidebar header (defaults to nav-link)
+  # nav-description: "#64748B"   # site description in sidebar header (defaults to nav-section-heading)
+  # nav-toggle: "#64748B"        # dark/light mode toggle (defaults to nav-section-heading)
   # divider: "#CBD5E1"           # border/hr colour (defaults to color-mix of background + text)
 
 dark:
@@ -26,6 +29,9 @@ dark:
   # nav-link: "#E2E8F0"          # inactive nav link text (defaults to text)
   # nav-link-active: "#60A5FA"   # active nav link text (defaults to accent)
   # nav-section-heading: "#94A3B8" # nav section label text (defaults to text-muted)
+  # nav-sitename: "#E2E8F0"      # site name in sidebar header (defaults to nav-link)
+  # nav-description: "#94A3B8"   # site description in sidebar header (defaults to nav-section-heading)
+  # nav-toggle: "#94A3B8"        # dark/light mode toggle (defaults to nav-section-heading)
   # divider: "#334155"           # border/hr colour (defaults to color-mix of background + text)
 
 # ──────────────────────────────────
diff --git a/docs/claude-design.md b/docs/claude-design.md
index f66c70c..375eb6e 100644
--- a/docs/claude-design.md
+++ b/docs/claude-design.md
@@ -21,10 +21,13 @@ light:
   nav-background: "#F8FAFC"   # sidebar/nav panel background
   text: "#1E293B"             # body text
   text-muted: "#64748B"       # secondary text, captions
-  nav-link: "#1E293B"         # inactive nav link text
-  nav-link-active: "#2563EB"  # active (current page) nav link text
+  nav-link: "#1E293B"           # inactive nav link text
+  nav-link-active: "#2563EB"    # active (current page) nav link text
   nav-section-heading: "#64748B"  # nav section label text (uppercase, small)
-  # divider: "#CBD5E1"        # omit to auto-derive via color-mix(background, text)
+  nav-sitename: "#1E293B"       # site name in sidebar header
+  nav-description: "#64748B"    # site description below the site name
+  nav-toggle: "#64748B"         # dark/light mode toggle button
+  # divider: "#CBD5E1"          # omit to auto-derive via color-mix(background, text)
 
 dark:
   accent: "#60A5FA"
@@ -35,7 +38,10 @@ dark:
   nav-link: "#E2E8F0"
   nav-link-active: "#60A5FA"
   nav-section-heading: "#94A3B8"
-  # divider: "#334155"        # omit to auto-derive via color-mix(background, text)
+  nav-sitename: "#E2E8F0"
+  nav-description: "#94A3B8"
+  nav-toggle: "#94A3B8"
+  # divider: "#334155"          # omit to auto-derive via color-mix(background, text)
 
 # ──────────────────────────────────
 # Semantic colours
@@ -95,38 +101,53 @@ nav-width: 20em
 
 ---
 
-## Critical rule: nav contrast
+## Nav colour keys: when to set them
 
-The renderer defaults `nav-link-active` to `accent` and `nav-link` to `text`.
-When `nav-background` and `accent` share the same hue (or are very close),
-active nav links become invisible — the coloured text disappears into a
-coloured background.
+There are six nav colour keys divided into two groups:
 
-The nav colour keys also control the **site name, site description, and
-dark/light mode toggle** — all three live inside the sidebar and inherit from
-the same variables. On muted or neutral nav backgrounds the content-area
-fallbacks (`text`, `text-muted`) are fine. On any saturated or bold nav
-background the contrast between `text` and `text-muted` is likely too low for
-these elements to remain legible, so all three nav colour keys must be set
-explicitly.
+**Nav links and labels** — control the navigation list itself:
+- `nav-link` — inactive link text (defaults to `text`)
+- `nav-link-active` — active/current page link text (defaults to `accent`)
+- `nav-section-heading` — uppercase section labels (defaults to `text-muted`)
 
-**Rule of thumb:** if `nav-background` has a saturation above roughly 20 % or
-a lightness below 30 % (dark sidebar) or above 85 % (near-white sidebar that
-differs noticeably from the page background), set `nav-link`,
-`nav-link-active`, and `nav-section-heading` explicitly for that mode.
+**Sidebar header elements** — control the branding area above the nav list:
+- `nav-sitename` — site name (defaults to `nav-link`)
+- `nav-description` — subtitle below the site name (defaults to `nav-section-heading`)
+- `nav-toggle` — dark/light mode toggle button (defaults to `nav-section-heading`)
 
-**Always set all three nav colour keys explicitly** whenever `nav-background`
-is anything other than a neutral near-white (light) or near-black (dark).
+### When the defaults are fine
+
+On themes where `nav-background` is a neutral near-white (light mode) or
+near-black (dark mode), `text` and `text-muted` read well against the nav
+background. All six keys can be omitted and the fallback chain works correctly.
+
+### When to set the keys explicitly
+
+Set all six keys whenever `nav-background` is anything other than a neutral:
+any saturated brand colour (red, navy, forest green, teal), any noticeably
+dark sidebar in an otherwise light design, or any light-but-tinted background.
+
+The two groups can be set independently. On a subtly tinted nav where the
+link defaults look fine but the site name needs slightly more weight or a
+different shade, set only the header keys (`nav-sitename`, `nav-description`,
+`nav-toggle`) and leave the nav link keys to their defaults.
+
+**Rule of thumb:** if `nav-background` has saturation above ~20 % or lightness
+below 30 % (dark sidebar) or differs from `background` by more than a slight
+tint, set all six explicitly for that mode.
 
 ### Pattern: accent-coloured nav (e.g. brand red, navy, forest green)
 
 ```yaml
 light:
   accent: "#D00C33"
-  nav-background: "#D00C33"   # same as accent — nav links MUST be overridden
+  nav-background: "#D00C33"      # same as accent — all nav keys must be set
   nav-link: "#FFFFFF"
   nav-link-active: "#FFFFFF"
   nav-section-heading: "rgba(255,255,255,0.65)"
+  nav-sitename: "#FFFFFF"
+  nav-description: "rgba(255,255,255,0.65)"
+  nav-toggle: "rgba(255,255,255,0.65)"
 
 dark:
   accent: "#D00C33"
@@ -134,6 +155,9 @@ dark:
   nav-link: "#E2E2E2"
   nav-link-active: "#FFFFFF"
   nav-section-heading: "#888888"
+  nav-sitename: "#FFFFFF"
+  nav-description: "#888888"
+  nav-toggle: "#888888"
 ```
 
 ### Pattern: dark nav in light mode (sidebar darker than content)
@@ -144,6 +168,9 @@ light:
   nav-link: "#CBD5E1"
   nav-link-active: "#FFFFFF"
   nav-section-heading: "#64748B"
+  nav-sitename: "#FFFFFF"
+  nav-description: "#64748B"
+  nav-toggle: "#64748B"
 ```
 
 ### Pattern: transparent / very light nav (default behaviour)
@@ -189,9 +216,10 @@ uses its own per-callout colour settings rather than the semantic variables.
 
 ## Checklist before finalising a theme
 
-- [ ] `nav-link`, `nav-link-active`, `nav-section-heading` specified for both
-      `light` and `dark` whenever `nav-background` is non-neutral
-- [ ] All three nav link colours contrast against `nav-background` (WCAG AA minimum)
+- [ ] All six nav colour keys (`nav-link`, `nav-link-active`, `nav-section-heading`,
+      `nav-sitename`, `nav-description`, `nav-toggle`) set for both `light` and
+      `dark` whenever `nav-background` is non-neutral
+- [ ] All nav colours contrast against `nav-background` (WCAG AA minimum)
 - [ ] `colours-semantic-dark` provided with lighter variants of each colour
 - [ ] `callouts` `primary-colour` matches `colours-semantic` values for consistency
 - [ ] `divider` omitted unless the auto-derived value looks wrong (check hr and table borders)