Merge pull request #98 from nesquena/sprint-26-themes

Sprint 26: Pluggable UI themes — dark, light, solarized, monokai, nord
2026-04-04 21:13:10 -07:00
parent d10871c0e4 82a942a2b1
commit 7bcd6623e9
11 changed files with 424 additions and 22 deletions
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,42 @@

 ---

+## [v0.34] Sprint 26 -- Pluggable UI Themes
+*April 5, 2026 | 433 tests*
+
+### Features
+- **6 built-in themes.** Dark (default), Light, Slate, Solarized Dark, Monokai,
+  Nord. Defined as CSS variable overrides on `:root[data-theme="name"]` — the
+  entire UI adapts automatically.
+- **Theme picker in Settings.** Dropdown with instant live preview. Changes
+  apply immediately as you click through options.
+- **`/theme` slash command.** `/theme dark`, `/theme light`, etc.
+- **Theme persistence.** Saved server-side in `settings.json` and client-side
+  in `localStorage` for flicker-free loading on page refresh.
+- **Flash prevention.** Inline `<script>` in `<head>` reads localStorage before
+  the stylesheet loads — no flash of the wrong theme.
+- **Custom theme support.** Any theme name is accepted (no enum gate). Create a
+  `:root[data-theme="name"]` CSS block and it works. See `THEMES.md`.
+- **Unsaved changes guard.** Settings panel now tracks dirty state and shows a
+  "You have unsaved changes" bar with Save/Discard buttons when closing with
+  unpersisted changes. Theme preview reverts on discard.
+
+### Architecture
+- `static/style.css`: 6 theme blocks using CSS variable overrides. Light theme
+  includes scrollbar and selection overrides.
+- `static/commands.js`: `/theme` command with validation.
+- `static/panels.js`: Settings dirty tracking, revert-on-discard, unsaved bar.
+- `static/boot.js`: Theme applied from server settings on boot.
+- `api/config.py`: `theme` field in `_SETTINGS_DEFAULTS` (no enum gate).
+- `THEMES.md`: Full documentation for creating custom themes.
+
+### Tests
+- 9 new tests in `test_sprint26.py`: default theme, round-trip persistence for
+  all 6 built-in themes, custom theme acceptance, settings isolation.
+  Total: **433 tests**.
+
+---
+
 ## [v0.33] /insights Sync + state.db Bridge Fix
 *April 5, 2026 | 424 tests*

@@ -1152,4 +1188,4 @@ Three-panel layout: sessions sidebar, chat area, workspace panel.

 ---

-*Last updated: v0.32, April 5, 2026 | Tests: 424*
+*Last updated: v0.34, April 5, 2026 | Tests: 433*
--- a/README.md
+++ b/README.md
@@ -314,17 +314,24 @@ across 22 test files.
 - 20MB POST body size limit
 - CDN resources pinned with SRI integrity hashes

+### Themes
+- 6 built-in themes: Dark (default), Light, Slate, Solarized Dark, Monokai, Nord
+- Switch via Settings panel dropdown (instant live preview) or `/theme` command
+- Persists across reloads (server-side in settings.json + localStorage for flicker-free loading)
+- Custom themes: define a `:root[data-theme="name"]` CSS block and it works — see [THEMES.md](THEMES.md)
+
 ### Settings and configuration
- Settings panel (gear icon) -- default model, default workspace, send key preference
+- Settings panel (gear icon) -- default model, default workspace, send key, theme
 - Send key: Enter (default) or Ctrl/Cmd+Enter
 - Show/hide CLI sessions toggle (enabled by default)
 - Token usage display toggle (off by default, also via `/usage` command)
+- Unsaved changes guard -- discard/save prompt when closing with unpersisted changes
 - Cron completion alerts -- toast notifications and unread badge on Tasks tab
 - Background agent error alerts -- banner when a non-active session encounters an error

 ### Slash commands
 - Type `/` in the composer for autocomplete dropdown
- Built-in: `/help`, `/clear`, `/model <name>`, `/workspace <name>`, `/new`, `/usage`
+- Built-in: `/help`, `/clear`, `/model <name>`, `/workspace <name>`, `/new`, `/usage`, `/theme`, `/compact`
 - Arrow keys navigate, Tab/Enter select, Escape closes
 - Unrecognized commands pass through to the agent

@@ -393,6 +400,7 @@ State lives outside the repo at `~/.hermes/webui-mvp/` by default
 - `TESTING.md` -- manual browser test plan and automated coverage reference
 - `CHANGELOG.md` -- release notes per sprint
 - `SPRINTS.md` -- forward sprint plan with CLI + Claude parity targets
+- `THEMES.md` -- theme system documentation, custom theme guide

 ## Repo

--- a/SPRINTS.md
+++ b/SPRINTS.md
@@ -1,6 +1,6 @@
 # Hermes Web UI -- Forward Sprint Plan

-> Current state: v0.32 | 424 tests | Daily driver ready
+> Current state: v0.34 | 433 tests | Daily driver ready
 > This document plans the path from here to two targets:
 >
 > Target A: 1:1 feature parity with the Hermes CLI (everything you can do from the
@@ -1156,6 +1156,6 @@ New test cases in `tests/test_sprint26.py`:
 ---

 *Last updated: April 5, 2026*
-*Current version: v0.33 | 424 tests*
+*Current version: v0.34 | 433 tests*
 *Next sprint: Sprint 24 (Web Polish + Bug Fix Pass)*
 *Horizon sprint: Sprint 26 (Pluggable UI Themes)*
--- a/THEMES.md
+++ b/THEMES.md
@@ -0,0 +1,117 @@
+# Hermes Web UI — Themes
+
+Hermes Web UI supports pluggable color themes. Five themes ship built-in, and
+you can create your own with pure CSS — no Python changes needed.
+
+---
+
+## Switching Themes
+
+**Settings panel:** Click the gear icon, select a theme from the dropdown. The
+preview is instant — the UI updates as you click through options.
+
+**Slash command:** Type `/theme dark` or `/theme light` in the composer.
+
+**Themes persist** across page reloads and server restarts (stored in
+`settings.json` server-side, with `localStorage` for flicker-free loading).
+
+---
+
+## Built-in Themes
+
+| Theme | Description |
+|-------|-------------|
+| **Dark** (default) | Deep navy/indigo with muted blue accents. Easy on the eyes for long sessions. |
+| **Light** | Warm off-white with dark text. High contrast for bright environments. |
+| **Slate** | Warm charcoal, lighter than Dark. Easier on the eyes for extended use. |
+| **Solarized Dark** | Ethan Schoonover's classic dark palette. Teal background, warm accents. |
+| **Monokai** | Warm dark theme inspired by the Monokai editor scheme. Green/pink accents. |
+| **Nord** | Arctic blue-gray palette from the Nord color system. Calm and minimal. |
+
+---
+
+## Creating a Custom Theme
+
+A theme is a CSS block that overrides the color variables. Add it to
+`static/style.css` (or a separate file that you link after the main stylesheet).
+
+### Step 1: Define your theme block
+
+Every color in the UI comes from these CSS variables:
+
+```css
+:root[data-theme="your-theme-name"] {
+  --bg: #1a1a2e;          /* Main background */
+  --sidebar: #16213e;      /* Sidebar background */
+  --border: rgba(255,255,255,0.08);   /* Subtle borders */
+  --border2: rgba(255,255,255,0.14);  /* Stronger borders */
+  --text: #e8e8f0;         /* Primary text color */
+  --muted: #8888aa;        /* Secondary/muted text */
+  --accent: #e94560;       /* Accent color (errors, warnings, delete) */
+  --blue: #7cb9ff;         /* Primary action color (links, active states) */
+  --gold: #c9a84c;         /* Secondary accent (pinned items, gold highlights) */
+  --code-bg: #0d1117;      /* Code block background */
+}
+```
+
+That's it. Override any or all of these variables. The entire UI adapts
+automatically because every color reference uses `var(--name)`.
+
+### Step 2: Add it to the theme picker (optional)
+
+To make your theme appear in the Settings dropdown, add an `<option>` to the
+theme `<select>` in `static/index.html`:
+
+```html
+<option value="your-theme-name">Your Theme Name</option>
+```
+
+And update the `/theme` command's valid theme list in `static/commands.js`.
+
+### Step 3: Test it
+
+Switch to your theme via `/theme your-theme-name` or the Settings panel.
+Check these areas:
+- Sidebar session list (hover states, active state, project borders)
+- Message bubbles (user vs assistant styling)
+- Code blocks (background contrast, copy button visibility)
+- Tool cards (running indicator, expand/collapse)
+- Settings panel and login page
+- Mobile layout (hamburger sidebar, bottom nav)
+
+### Tips
+
+- **Light themes** need additional scrollbar overrides to avoid dark scrollbars
+  on a light background. See the built-in light theme for the pattern.
+- The **logo gradient** uses `--accent` automatically, so it adapts to your
+  theme without extra work.
+- **Prism.js syntax highlighting** uses its own CDN stylesheet (Tomorrow theme).
+  It works well on dark themes; on light themes the contrast is acceptable but
+  not perfect. Custom Prism theme support is planned for a future update.
+- **No server changes needed.** The `theme` setting in `settings.json` accepts
+  any string — your custom theme name will persist without code changes.
+
+---
+
+## How Themes Work Internally
+
+1. Each theme is a `:root[data-theme="name"]` CSS block that overrides variables.
+2. Switching themes sets `document.documentElement.dataset.theme = name` in JS.
+3. A tiny inline `<script>` in `<head>` reads `localStorage` before the
+   stylesheet loads — this prevents a flash of the wrong theme on page load.
+4. The theme preference is saved server-side via `POST /api/settings` and
+   loaded on boot via `GET /api/settings`.
+5. The `/theme` command and Settings dropdown both update the DOM, localStorage,
+   and server settings simultaneously.
+
+---
+
+## Contributing a Theme
+
+To contribute a new built-in theme:
+
+1. Add your `:root[data-theme="name"]` block to `static/style.css`
+2. Add the `<option>` to the Settings panel in `static/index.html`
+3. Add the theme name to the valid list in `cmdTheme()` in `static/commands.js`
+4. Test on desktop and mobile
+5. Open a PR — themes are pure CSS additions with no backend changes needed
--- a/api/config.py
+++ b/api/config.py
@@ -653,6 +653,7 @@ _SETTINGS_DEFAULTS = {
    'show_token_usage': False,  # show input/output token badge below assistant messages
    'show_cli_sessions': False,  # merge CLI sessions from state.db into the sidebar
    'sync_to_insights': False,  # mirror WebUI token usage to state.db for /insights
+    'theme': 'dark',  # active UI theme name (no enum gate -- allows custom themes)
    'password_hash': None,  # SHA-256 hash; None = auth disabled
 }

--- a/static/boot.js
+++ b/static/boot.js
@@ -226,7 +226,7 @@ document.addEventListener('keydown',async e=>{
  if(e.key==='Escape'){
    // Close settings overlay if open
    const settingsOverlay=$('settingsOverlay');
-    if(settingsOverlay&&settingsOverlay.style.display!=='none'){toggleSettings();return;}
+    if(settingsOverlay&&settingsOverlay.style.display!=='none'){_closeSettingsPanel();return;}
    // Close workspace dropdown
    closeWsDropdown();
    // Clear session search
@@ -308,7 +308,7 @@ document.querySelectorAll('.suggestion').forEach(btn=>{

 (async()=>{
  // Load send key preference
-  try{const s=await api('/api/settings');window._sendKey=s.send_key||'enter';window._showTokenUsage=!!s.show_token_usage;window._showCliSessions=!!s.show_cli_sessions;}catch(e){window._sendKey='enter';window._showTokenUsage=false;window._showCliSessions=false;}
+  try{const s=await api('/api/settings');window._sendKey=s.send_key||'enter';window._showTokenUsage=!!s.show_token_usage;window._showCliSessions=!!s.show_cli_sessions;const _theme=s.theme||'dark';document.documentElement.dataset.theme=_theme;localStorage.setItem('hermes-theme',_theme);}catch(e){window._sendKey='enter';window._showTokenUsage=false;window._showCliSessions=false;}
  // Fetch active profile
  try{const p=await api('/api/profile/active');S.activeProfile=p.name||'default';}catch(e){S.activeProfile='default';}
  // Update profile chip label immediately
--- a/static/commands.js
+++ b/static/commands.js
@@ -10,6 +10,7 @@ const COMMANDS=[
  {name:'workspace', desc:'Switch workspace by name',            fn:cmdWorkspace, arg:'name'},
  {name:'new',       desc:'Start a new chat session',            fn:cmdNew},
  {name:'usage',     desc:'Toggle token usage display on/off',   fn:cmdUsage},
+  {name:'theme',     desc:'Switch theme (dark/light/slate/solarized/monokai/nord)', fn:cmdTheme, arg:'name'},
 ];

 function parseCommand(text){
@@ -122,6 +123,22 @@ async function cmdUsage(){
  showToast('Token usage '+(next?'on':'off'));
 }

+async function cmdTheme(args){
+  const themes=['dark','light','slate','solarized','monokai','nord'];
+  if(!args||!themes.includes(args.toLowerCase())){
+    showToast('Usage: /theme '+themes.join('|'));
+    return;
+  }
+  const t=args.toLowerCase();
+  document.documentElement.dataset.theme=t;
+  localStorage.setItem('hermes-theme',t);
+  try{await api('/api/settings',{method:'POST',body:JSON.stringify({theme:t})});}catch(e){}
+  // Update settings dropdown if panel is open
+  const sel=$('settingsTheme');
+  if(sel)sel.value=t;
+  showToast('Theme: '+t);
+}
+
 // ── Autocomplete dropdown ───────────────────────────────────────────────────

 let _cmdSelectedIdx=-1;
--- a/static/index.html
+++ b/static/index.html
@@ -4,6 +4,7 @@
 <meta charset="utf-8">
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <title>Hermes</title>
+<script>(function(){var t=localStorage.getItem('hermes-theme');if(t&&t!=='dark')document.documentElement.dataset.theme=t;})()</script>
 <link rel="stylesheet" href="/static/style.css">
  <!-- Prism.js syntax highlighting (loaded async, non-blocking) -->
  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/prismjs@1.29.0/themes/prism-tomorrow.min.css" integrity="sha384-wFjoQjtV1y5jVHbt0p35Ui8aV8GVpEZkyF99OXWqP/eNJDU93D3Ugxkoyh6Y2I4A" crossorigin="anonymous">
@@ -13,7 +14,7 @@
 <body>
 <div class="layout">
  <aside class="sidebar">
-    <div class="sidebar-header"><div class="logo">H</div><div><h1 style="margin:0;font-size:15px;font-weight:700;letter-spacing:-.01em">Hermes</h1><div style="font-size:10px;color:var(--muted);opacity:.8;margin-top:1px">v0.33</div></div></div>
+    <div class="sidebar-header"><div class="logo">H</div><div><h1 style="margin:0;font-size:15px;font-weight:700;letter-spacing:-.01em">Hermes</h1><div style="font-size:10px;color:var(--muted);opacity:.8;margin-top:1px">v0.34</div></div></div>
    <div class="sidebar-nav">
      <button class="nav-tab active" data-panel="chat" data-label="Chat" onclick="switchPanel('chat')" title="Chat">&#128172;</button>
      <button class="nav-tab" data-panel="tasks" data-label="Tasks" onclick="switchPanel('tasks')" title="Tasks">&#128197;</button>
@@ -311,7 +312,7 @@
  <div class="settings-panel">
    <div class="settings-header">
      <h3 style="margin:0;font-size:16px">Settings</h3>
-      <button class="panel-icon-btn" onclick="toggleSettings()" title="Close">&#10005;</button>
+      <button class="panel-icon-btn" onclick="_closeSettingsPanel()" title="Close">&#10005;</button>
    </div>
    <div class="settings-body">
      <div class="settings-field">
@@ -329,6 +330,17 @@
          <option value="ctrl+enter">Ctrl+Enter (Enter for newline)</option>
        </select>
      </div>
+      <div class="settings-field">
+        <label for="settingsTheme">Theme</label>
+        <select id="settingsTheme" style="width:100%;padding:8px;background:var(--code-bg);color:var(--text);border:1px solid var(--border2);border-radius:6px" onchange="document.documentElement.dataset.theme=this.value;localStorage.setItem('hermes-theme',this.value)">
+          <option value="dark">Dark (default)</option>
+          <option value="light">Light</option>
+          <option value="slate">Slate (charcoal)</option>
+          <option value="solarized">Solarized Dark</option>
+          <option value="monokai">Monokai</option>
+          <option value="nord">Nord</option>
+        </select>
+      </div>
      <div class="settings-field">
        <label style="display:flex;align-items:center;gap:8px;cursor:pointer">
          <input type="checkbox" id="settingsShowTokenUsage" style="width:15px;height:15px;accent-color:var(--accent)">
--- a/static/panels.js
+++ b/static/panels.js
@@ -908,17 +908,70 @@ document.addEventListener('drop',e=>{e.preventDefault();dragCounter=0;wrap.class

 // ── Settings panel ───────────────────────────────────────────────────────────

+let _settingsDirty = false;
+let _settingsThemeOnOpen = null; // track theme at open time for discard revert
+
 function toggleSettings(){
  const overlay=$('settingsOverlay');
  if(!overlay) return;
  if(overlay.style.display==='none'){
+    _settingsDirty = false;
+    _settingsThemeOnOpen = document.documentElement.dataset.theme || 'dark';
    overlay.style.display='';
    loadSettingsPanel();
  } else {
-    overlay.style.display='none';
+    _closeSettingsPanel();
  }
 }

+// Close with unsaved-changes check. If dirty, show a confirm dialog.
+function _closeSettingsPanel(){
+  if(!_settingsDirty){
+    // Nothing changed -- revert any live preview and close
+    _revertSettingsPreview();
+    $('settingsOverlay').style.display='none';
+    return;
+  }
+  // Dirty -- show inline confirm bar
+  _showSettingsUnsavedBar();
+}
+
+// Revert live DOM/localStorage to what they were when the panel opened
+function _revertSettingsPreview(){
+  if(_settingsThemeOnOpen){
+    document.documentElement.dataset.theme = _settingsThemeOnOpen;
+    localStorage.setItem('hermes-theme', _settingsThemeOnOpen);
+  }
+}
+
+// Show the "Unsaved changes" bar inside the settings panel
+function _showSettingsUnsavedBar(){
+  let bar = $('settingsUnsavedBar');
+  if(bar){ bar.style.display=''; return; }
+  // Create it
+  bar = document.createElement('div');
+  bar.id = 'settingsUnsavedBar';
+  bar.style.cssText = 'display:flex;align-items:center;justify-content:space-between;gap:8px;background:rgba(233,69,96,.12);border:1px solid rgba(233,69,96,.3);border-radius:8px;padding:10px 14px;margin:0 0 12px;font-size:13px;';
+  bar.innerHTML = '<span style="color:var(--text)">You have unsaved changes.</span>'
+    + '<span style="display:flex;gap:8px">'
+    + '<button onclick="_discardSettings()" style="padding:5px 12px;border-radius:6px;border:1px solid var(--border2);background:rgba(255,255,255,.06);color:var(--muted);cursor:pointer;font-size:12px;font-weight:600">Discard</button>'
+    + '<button onclick="saveSettings(true)" style="padding:5px 12px;border-radius:6px;border:none;background:var(--accent);color:#fff;cursor:pointer;font-size:12px;font-weight:600">Save</button>'
+    + '</span>';
+  const body = document.querySelector('.settings-body') || document.querySelector('.settings-panel');
+  if(body) body.prepend(bar);
+}
+
+function _discardSettings(){
+  _revertSettingsPreview();
+  _settingsDirty = false;
+  $('settingsOverlay').style.display = 'none';
+}
+
+// Mark settings as dirty whenever anything changes
+function _markSettingsDirty(){
+  _settingsDirty = true;
+}
+
 async function loadSettingsPanel(){
  try{
    const settings=await api('/api/settings');
@@ -940,6 +993,7 @@ async function loadSettingsPanel(){
        }
      }catch(e){}
      modelSel.value=settings.default_model||'';
+      modelSel.addEventListener('change',_markSettingsDirty,{once:false});
    }
    // Populate workspace dropdown from /api/workspaces
    const wsSel=$('settingsWorkspace');
@@ -954,19 +1008,23 @@ async function loadSettingsPanel(){
        }
      }catch(e){}
      wsSel.value=settings.default_workspace||'';
+      wsSel.addEventListener('change',_markSettingsDirty,{once:false});
    }
    // Send key preference
    const sendKeySel=$('settingsSendKey');
-    if(sendKeySel) sendKeySel.value=settings.send_key||'enter';
+    if(sendKeySel){sendKeySel.value=settings.send_key||'enter';sendKeySel.addEventListener('change',_markSettingsDirty,{once:false});}
+    // Theme preference
+    const themeSel=$('settingsTheme');
+    if(themeSel){themeSel.value=settings.theme||'dark';themeSel.addEventListener('change',_markSettingsDirty,{once:false});}
    const showUsageCb=$('settingsShowTokenUsage');
-    if(showUsageCb) showUsageCb.checked=!!settings.show_token_usage;
+    if(showUsageCb){showUsageCb.checked=!!settings.show_token_usage;showUsageCb.addEventListener('change',_markSettingsDirty,{once:false});}
    const showCliCb=$('settingsShowCliSessions');
-    if(showCliCb) showCliCb.checked=!!settings.show_cli_sessions;
+    if(showCliCb){showCliCb.checked=!!settings.show_cli_sessions;showCliCb.addEventListener('change',_markSettingsDirty,{once:false});}
    const syncCb=$('settingsSyncInsights');
-    if(syncCb) syncCb.checked=!!settings.sync_to_insights;
+    if(syncCb){syncCb.checked=!!settings.sync_to_insights;syncCb.addEventListener('change',_markSettingsDirty,{once:false});}
    // Password field: always blank (we don't send hash back)
    const pwField=$('settingsPassword');
-    if(pwField) pwField.value='';
+    if(pwField){pwField.value='';pwField.addEventListener('input',_markSettingsDirty,{once:false});}
    // Show auth buttons only when auth is active
    try{
      const authStatus=await api('/api/auth/status');
@@ -981,17 +1039,19 @@ async function loadSettingsPanel(){
  }
 }

-async function saveSettings(){
+async function saveSettings(andClose){
  const model=($('settingsModel')||{}).value;
  const workspace=($('settingsWorkspace')||{}).value;
  const sendKey=($('settingsSendKey')||{}).value;
  const showTokenUsage=!!($('settingsShowTokenUsage')||{}).checked;
  const showCliSessions=!!($('settingsShowCliSessions')||{}).checked;
  const pw=($('settingsPassword')||{}).value;
+  const theme=($('settingsTheme')||{}).value||'dark';
  const body={};
  if(model) body.default_model=model;
  if(workspace) body.default_workspace=workspace;
  if(sendKey) body.send_key=sendKey;
+  body.theme=theme;
  body.show_token_usage=showTokenUsage;
  body.show_cli_sessions=showCliSessions;
  body.sync_to_insights=!!($('settingsSyncInsights')||{}).checked;
@@ -1002,7 +1062,9 @@ async function saveSettings(){
      window._sendKey=sendKey||'enter';
      window._showTokenUsage=showTokenUsage;
      showToast('Settings saved (password set — login now required)');
-      toggleSettings();
+      _settingsDirty=false; _settingsThemeOnOpen=theme;
+      const bar=$('settingsUnsavedBar'); if(bar) bar.style.display='none';
+      $('settingsOverlay').style.display='none';
      return;
    }catch(e){showToast('Save failed: '+e.message);return;}
  }
@@ -1011,10 +1073,12 @@ async function saveSettings(){
    window._sendKey=sendKey||'enter';
    window._showTokenUsage=showTokenUsage;
    window._showCliSessions=showCliSessions;
+    _settingsDirty=false; _settingsThemeOnOpen=theme;
+    const bar=$('settingsUnsavedBar'); if(bar) bar.style.display='none';
    renderMessages();
    if(typeof renderSessionList==='function') renderSessionList();
    showToast('Settings saved');
-    toggleSettings();
+    $('settingsOverlay').style.display='none';
  }catch(e){
    showToast('Save failed: '+e.message);
  }
@@ -1044,10 +1108,10 @@ async function disableAuth(){
  }
 }

-// Close settings on overlay click (not panel click)
+// Close settings on overlay click (not panel click) -- with unsaved-changes check
 document.addEventListener('click',e=>{
  const overlay=$('settingsOverlay');
-  if(overlay&&e.target===overlay) toggleSettings();
+  if(overlay&&e.target===overlay) _closeSettingsPanel();
 });

 // ── Cron completion alerts ────────────────────────────────────────────────────
--- a/static/style.css
+++ b/static/style.css
@@ -4,6 +4,34 @@
    --text:#e8e8f0;--muted:#8888aa;--accent:#e94560;--blue:#7cb9ff;--gold:#c9a84c;--code-bg:#0d1117;
    font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",system-ui,sans-serif;font-size:14px;line-height:1.6;
  }
+  /* ── Slate theme (warm charcoal, lighter than dark, easier on the eyes) ── */
+  :root[data-theme="slate"]{
+    --bg:#2b2d30;--sidebar:#25272b;--border:rgba(255,255,255,0.09);--border2:rgba(255,255,255,0.16);
+    --text:#d4d4d8;--muted:#8a8a9a;--accent:#e06c75;--blue:#82aaff;--gold:#d4a85a;--code-bg:#1e2023;
+  }
+  /* ── Light theme (warm off-white, softer than pure white) ── */
+  :root[data-theme="light"]{
+    --bg:#f0ede8;--sidebar:#e4e0d8;--border:rgba(0,0,0,0.09);--border2:rgba(0,0,0,0.15);
+    --text:#2c2825;--muted:#7a746a;--accent:#b5451b;--blue:#2d6fa3;--gold:#8a6520;--code-bg:#e8e4de;
+  }
+  :root[data-theme="light"] ::-webkit-scrollbar-thumb{background:rgba(0,0,0,.15);}
+  :root[data-theme="light"] ::-webkit-scrollbar-thumb:hover{background:rgba(0,0,0,.3);}
+  :root[data-theme="light"] ::selection{background:rgba(45,111,163,.2);}
+  /* ── Solarized Dark theme ── */
+  :root[data-theme="solarized"]{
+    --bg:#002b36;--sidebar:#073642;--border:rgba(255,255,255,0.08);--border2:rgba(255,255,255,0.13);
+    --text:#839496;--muted:#657b83;--accent:#dc322f;--blue:#268bd2;--gold:#b58900;--code-bg:#073642;
+  }
+  /* ── Monokai theme ── */
+  :root[data-theme="monokai"]{
+    --bg:#272822;--sidebar:#1e1f1c;--border:rgba(255,255,255,0.07);--border2:rgba(255,255,255,0.12);
+    --text:#f8f8f2;--muted:#75715e;--accent:#f92672;--blue:#66d9e8;--gold:#e6db74;--code-bg:#1e1f1c;
+  }
+  /* ── Nord theme ── */
+  :root[data-theme="nord"]{
+    --bg:#2e3440;--sidebar:#272c36;--border:rgba(255,255,255,0.07);--border2:rgba(255,255,255,0.12);
+    --text:#eceff4;--muted:#9099aa;--accent:#bf616a;--blue:#81a1c1;--gold:#ebcb8b;--code-bg:#272c36;
+  }
  body{background:var(--bg);color:var(--text);height:100vh;height:100dvh;overflow:hidden;display:flex;}
  .layout{display:flex;width:100%;height:100vh;height:100dvh;}
  .sidebar{width:300px;background:var(--sidebar);border-right:1px solid var(--border);display:flex;flex-direction:column;overflow:visible;flex-shrink:0;}
@@ -353,7 +381,7 @@
    /* Tool cards */
    .tool-card{margin-left:0!important;font-size:12px;}
    /* Settings modal */
-    .settings-panel{width:95vw;max-width:95vw;}
+    .settings-panel{width:95vw;max-width:95vw;min-height:min(580px,88vh);max-height:92vh;}
    /* Login page responsive */
    .card{width:90vw;max-width:320px;padding:28px 24px;}
  }
@@ -624,7 +652,7 @@ body.resizing{user-select:none;cursor:col-resize;}

 /* ── Settings overlay ── */
 .settings-overlay{position:fixed;inset:0;background:rgba(0,0,0,.5);z-index:1000;display:flex;align-items:center;justify-content:center;}
-.settings-panel{background:var(--bg);border:1px solid var(--border);border-radius:12px;padding:0;width:380px;max-width:90vw;max-height:80vh;overflow:visible;box-shadow:0 12px 40px rgba(0,0,0,.5);display:flex;flex-direction:column;}
+.settings-panel{background:var(--bg);border:1px solid var(--border);border-radius:12px;padding:0;width:420px;max-width:92vw;max-height:92vh;min-height:min(680px,90vh);overflow:visible;box-shadow:0 12px 40px rgba(0,0,0,.5);display:flex;flex-direction:column;}
 .settings-header{display:flex;align-items:center;justify-content:space-between;padding:16px 20px 12px;border-bottom:1px solid var(--border);}
 .settings-body{padding:20px;overflow-y:auto;flex:1;}
 .settings-field{margin-bottom:16px;}
--- a/tests/test_sprint26.py
+++ b/tests/test_sprint26.py
@@ -0,0 +1,119 @@
+"""
+Sprint 26 Tests: pluggable UI themes — settings persistence, theme default,
+custom theme names accepted.
+"""
+import json, urllib.error, urllib.request
+
+BASE = "http://127.0.0.1:8788"
+
+
+def get(path):
+    with urllib.request.urlopen(BASE + path, timeout=10) as r:
+        return json.loads(r.read()), r.status
+
+
+def post(path, body=None):
+    data = json.dumps(body or {}).encode()
+    req = urllib.request.Request(BASE + path, data=data,
+                                headers={"Content-Type": "application/json"})
+    try:
+        with urllib.request.urlopen(req, timeout=10) as r:
+            return json.loads(r.read()), r.status
+    except urllib.error.HTTPError as e:
+        return json.loads(e.read()), e.code
+
+
+# ── Theme settings ───────────────────────────────────────────────────────
+
+def test_settings_default_theme():
+    """Default theme should be 'dark'."""
+    d, status = get("/api/settings")
+    assert status == 200
+    assert d.get("theme") == "dark"
+
+
+def test_settings_set_theme_light():
+    """Setting theme to 'light' should persist and round-trip."""
+    try:
+        d, status = post("/api/settings", {"theme": "light"})
+        assert status == 200
+        d2, _ = get("/api/settings")
+        assert d2.get("theme") == "light"
+    finally:
+        # Reset to dark
+        post("/api/settings", {"theme": "dark"})
+
+
+def test_settings_set_theme_solarized():
+    """Setting theme to 'solarized' should persist."""
+    try:
+        post("/api/settings", {"theme": "solarized"})
+        d, _ = get("/api/settings")
+        assert d.get("theme") == "solarized"
+    finally:
+        post("/api/settings", {"theme": "dark"})
+
+
+def test_settings_set_theme_monokai():
+    """Setting theme to 'monokai' should persist."""
+    try:
+        post("/api/settings", {"theme": "monokai"})
+        d, _ = get("/api/settings")
+        assert d.get("theme") == "monokai"
+    finally:
+        post("/api/settings", {"theme": "dark"})
+
+
+def test_settings_set_theme_nord():
+    """Setting theme to 'nord' should persist."""
+    try:
+        post("/api/settings", {"theme": "nord"})
+        d, _ = get("/api/settings")
+        assert d.get("theme") == "nord"
+    finally:
+        post("/api/settings", {"theme": "dark"})
+
+
+def test_settings_set_theme_slate():
+    """Setting theme to 'slate' should persist."""
+    try:
+        post("/api/settings", {"theme": "slate"})
+        d, _ = get("/api/settings")
+        assert d.get("theme") == "slate"
+    finally:
+        post("/api/settings", {"theme": "dark"})
+
+
+def test_settings_custom_theme_accepted():
+    """Custom theme names should be accepted (no enum gate)."""
+    try:
+        d, status = post("/api/settings", {"theme": "my-custom-theme"})
+        assert status == 200
+        d2, _ = get("/api/settings")
+        assert d2.get("theme") == "my-custom-theme"
+    finally:
+        post("/api/settings", {"theme": "dark"})
+
+
+def test_theme_does_not_break_other_settings():
+    """Setting theme should not disturb other settings."""
+    d_before, _ = get("/api/settings")
+    send_key_before = d_before.get("send_key")
+    try:
+        post("/api/settings", {"theme": "nord"})
+        d_after, _ = get("/api/settings")
+        assert d_after.get("send_key") == send_key_before
+        assert d_after.get("theme") == "nord"
+    finally:
+        post("/api/settings", {"theme": "dark"})
+
+
+def test_theme_survives_round_trip():
+    """Theme set via POST should appear in subsequent GET."""
+    try:
+        post("/api/settings", {"theme": "monokai"})
+        d, status = get("/api/settings")
+        assert status == 200
+        assert d["theme"] == "monokai"
+    finally:
+        post("/api/settings", {"theme": "dark"})