diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9370134..14be64d 100644
--- 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*
diff --git a/README.md b/README.md
index 9f594d8..736091e 100644
--- 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
 
diff --git a/SPRINTS.md b/SPRINTS.md
index 41755dd..bdd9dbf 100644
--- 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)*
diff --git a/THEMES.md b/THEMES.md
index 1d10aaf..9c4dfe6 100644
--- a/THEMES.md
+++ b/THEMES.md
@@ -22,7 +22,8 @@ preview is instant — the UI updates as you click through options.
 | Theme | Description |
 |-------|-------------|
 | **Dark** (default) | Deep navy/indigo with muted blue accents. Easy on the eyes for long sessions. |
-| **Light** | Clean white/gray with dark text. High contrast for bright environments. |
+| **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. |
diff --git a/static/commands.js b/static/commands.js
index 2921037..87844c2 100644
--- a/static/commands.js
+++ b/static/commands.js
@@ -10,7 +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/solarized/monokai/nord)', fn:cmdTheme, arg:'name'},
+  {name:'theme',     desc:'Switch theme (dark/light/slate/solarized/monokai/nord)', fn:cmdTheme, arg:'name'},
 ];
 
 function parseCommand(text){
@@ -124,7 +124,7 @@ async function cmdUsage(){
 }
 
 async function cmdTheme(args){
-  const themes=['dark','slate','solarized','monokai','nord'];
+  const themes=['dark','light','slate','solarized','monokai','nord'];
   if(!args||!themes.includes(args.toLowerCase())){
     showToast('Usage: /theme '+themes.join('|'));
     return;
diff --git a/static/index.html b/static/index.html
index 77980dd..2da6b4a 100644
--- a/static/index.html
+++ b/static/index.html
@@ -14,7 +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>
@@ -334,6 +334,7 @@
         <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>
