diff --git a/src/pages/mystery.astro b/src/pages/mystery.astro
index 3af1f10..236b8f5 100644
--- a/src/pages/mystery.astro
+++ b/src/pages/mystery.astro
@@ -43,6 +43,7 @@ import '../mystery/ui/crt.css'
     </script>
     <script>
       import '../mystery/ui/terminal.ts'
+      import '../mystery/ui/theme.ts'
     </script>
   </body>
 </html>
diff --git a/src/ui/terminal.ts b/src/ui/terminal.ts
index bf54265..b10a30c 100644
--- a/src/ui/terminal.ts
+++ b/src/ui/terminal.ts
@@ -23,6 +23,47 @@ if (!transcriptEl || !inputEl) {
     state = initialStateFor(world)
   }
 
+  const buildParserContext = (s: GameState): ParserContext => {
+    const room = world.rooms[s.location]
+    const visibleNouns: { id: string; aliases: string[] }[] = []
+    if (room) {
+      for (const id of room.items) {
+        const it = world.items[id]
+        if (it) visibleNouns.push({ id, aliases: it.names })
+      }
+      if (room.encounter && s.encounterState[room.encounter]) {
+        visibleNouns.push({ id: room.encounter, aliases: [room.encounter] })
+      }
+    }
+    for (const inst of s.inventory) {
+      const it = world.items[inst.id]
+      if (it) visibleNouns.push({ id: inst.id, aliases: it.names })
+    }
+    return {
+      knownItems: Object.keys(world.items),
+      knownEncounters: Object.keys(world.encounters),
+      visibleNouns,
+      inventoryItemIds: s.inventory.map((i) => i.id),
+      lastNoun: s.lastNoun,
+      awaitingDisambiguation: s.pendingDisambiguation,
+    }
+  }
+
+  const renderAll = (lines: TranscriptLine[]): void => {
+    if (!transcriptEl) return
+    for (const line of lines) {
+      const el = document.createElement('div')
+      el.className = line.kind
+      el.textContent = line.text
+      transcriptEl.appendChild(el)
+    }
+    transcriptEl.scrollTop = transcriptEl.scrollHeight
+  }
+
+  const appendLines = (lines: TranscriptLine[]): void => {
+    renderAll(lines)
+  }
+
   renderAll(state.transcript)
   inputEl.focus()
 
@@ -76,6 +117,9 @@ if (!transcriptEl || !inputEl) {
       appendLines(result.appended)
       saveState(state)
       transcriptEl.scrollTop = transcriptEl.scrollHeight
+      if (raw.trim().toLowerCase() === 'theme') {
+        document.dispatchEvent(new CustomEvent('halfstreet-toggle-theme'))
+      }
     } catch (err) {
       console.error('[halfstreet] dispatch error', err)
       appendLines([{ kind: 'system', text: '[ The terminal hums and resets. ]' }])
@@ -88,45 +132,4 @@ if (!transcriptEl || !inputEl) {
       window.location.href = '/'
     }
   })
-
-  function buildParserContext(s: GameState): ParserContext {
-    const room = world.rooms[s.location]
-    const visibleNouns: { id: string; aliases: string[] }[] = []
-    if (room) {
-      for (const id of room.items) {
-        const it = world.items[id]
-        if (it) visibleNouns.push({ id, aliases: it.names })
-      }
-      if (room.encounter && s.encounterState[room.encounter]) {
-        visibleNouns.push({ id: room.encounter, aliases: [room.encounter] })
-      }
-    }
-    for (const inst of s.inventory) {
-      const it = world.items[inst.id]
-      if (it) visibleNouns.push({ id: inst.id, aliases: it.names })
-    }
-    return {
-      knownItems: Object.keys(world.items),
-      knownEncounters: Object.keys(world.encounters),
-      visibleNouns,
-      inventoryItemIds: s.inventory.map((i) => i.id),
-      lastNoun: s.lastNoun,
-      awaitingDisambiguation: s.pendingDisambiguation,
-    }
-  }
-
-  function renderAll(lines: TranscriptLine[]): void {
-    if (!transcriptEl) return
-    for (const line of lines) {
-      const el = document.createElement('div')
-      el.className = line.kind
-      el.textContent = line.text
-      transcriptEl.appendChild(el)
-    }
-    transcriptEl.scrollTop = transcriptEl.scrollHeight
-  }
-
-  function appendLines(lines: TranscriptLine[]): void {
-    renderAll(lines)
-  }
 }
diff --git a/src/ui/theme.ts b/src/ui/theme.ts
new file mode 100644
index 0000000..57a27f3
--- /dev/null
+++ b/src/ui/theme.ts
@@ -0,0 +1,42 @@
+const STORAGE_KEY = 'halfstreet:theme:v1'
+
+type Theme = 'amber' | 'ansi'
+
+function getStored(): Theme {
+  try {
+    return (localStorage.getItem(STORAGE_KEY) as Theme | null) === 'ansi' ? 'ansi' : 'amber'
+  } catch {
+    return 'amber'
+  }
+}
+
+function setTheme(theme: Theme): void {
+  document.documentElement.setAttribute('data-mystery-theme', theme)
+  try {
+    localStorage.setItem(STORAGE_KEY, theme)
+  } catch {
+    // ignore
+  }
+  for (const btn of document.querySelectorAll<HTMLButtonElement>('[data-theme-choice]')) {
+    btn.setAttribute('aria-pressed', btn.dataset['themeChoice'] === theme ? 'true' : 'false')
+  }
+}
+
+const initial = getStored()
+setTheme(initial)
+
+document.querySelectorAll<HTMLButtonElement>('[data-theme-choice]').forEach((btn) => {
+  btn.addEventListener('click', () => {
+    const next = (btn.dataset['themeChoice'] as Theme | undefined) ?? 'amber'
+    setTheme(next)
+  })
+})
+
+// Allow the engine's `theme` meta-command (handled in terminal.ts) to flip
+// without going through the button by listening for a custom event.
+document.addEventListener('halfstreet-toggle-theme', () => {
+  const current = (document.documentElement.getAttribute('data-mystery-theme') as Theme | null) ?? 'amber'
+  setTheme(current === 'amber' ? 'ansi' : 'amber')
+})
+
+export {}