diff --git a/packages/collab-web/index.html b/packages/collab-web/index.html
index 37fdefd1b..12e868d3f 100644
--- a/packages/collab-web/index.html
+++ b/packages/collab-web/index.html
@@ -3,8 +3,9 @@
 	<head>
 		<meta charset="utf-8" />
 		<meta name="viewport" content="width=device-width, initial-scale=1" />
-		<meta name="color-scheme" content="dark" />
-		<meta name="theme-color" content="#0f0b14" />
+		<meta name="color-scheme" content="light dark" />
+		<meta name="theme-color" media="(prefers-color-scheme: light)" content="#faf7fc" />
+		<meta name="theme-color" media="(prefers-color-scheme: dark)" content="#0f0b14" />
 
 		<title>omp collab — live agent session in your browser</title>
 		<meta
@@ -69,6 +70,7 @@
 	</head>
 	<body>
 		<div id="root"></div>
+		<script>(function(){try{var s=localStorage.getItem("omp-collab-theme");var sys=matchMedia("(prefers-color-scheme: dark)").matches?"dark":"light";var t=(s==="light"||s==="dark")?s:sys;document.documentElement.dataset.theme=t;document.documentElement.style.colorScheme=t;}catch(e){}})();</script>
 		<script type="module" src="./src/main.tsx"></script>
 	</body>
 </html>
diff --git a/packages/collab-web/src/components/shell/ConnectScreen.tsx b/packages/collab-web/src/components/shell/ConnectScreen.tsx
index 8e3e1fdf2..0965ffca7 100644
--- a/packages/collab-web/src/components/shell/ConnectScreen.tsx
+++ b/packages/collab-web/src/components/shell/ConnectScreen.tsx
@@ -1,5 +1,6 @@
 import type { FormEvent, ReactNode } from "react";
 import { useState } from "react";
+import { ThemeToggle } from "./ThemeToggle";
 
 export interface ConnectScreenProps {
 	defaultName: string;
@@ -28,9 +29,14 @@ export function ConnectScreen({ defaultName, error, onConnect }: ConnectScreenPr
 	return (
 		<div className="sh-connect">
 			<form className="sh-connect-card" onSubmit={submit}>
-				<div className="sh-lockup">
-					<span className="sh-lockup-pi">π</span> omp collab
+				<div className="sh-connect-head">
+					<div className="sh-lockup">
+						<span className="sh-lockup-mark" aria-hidden="true" />
+						<span className="sh-lockup-pi">π</span> omp collab
+					</div>
+					<ThemeToggle />
 				</div>
+				<div className="sh-connect-sub">live agent session, in your browser</div>
 				<label className="sh-field">
 					<span className="sh-field-label">join link</span>
 					<input
@@ -43,6 +49,7 @@ export function ConnectScreen({ defaultName, error, onConnect }: ConnectScreenPr
 						autoComplete="off"
 						autoFocus
 					/>
+					<span className="sh-field-hint">paste a /collab link from any omp session</span>
 				</label>
 				<label className="sh-field">
 					<span className="sh-field-label">display name</span>
diff --git a/packages/collab-web/src/components/shell/HeaderBar.tsx b/packages/collab-web/src/components/shell/HeaderBar.tsx
index cc64e6f8f..c1c9d5159 100644
--- a/packages/collab-web/src/components/shell/HeaderBar.tsx
+++ b/packages/collab-web/src/components/shell/HeaderBar.tsx
@@ -2,6 +2,7 @@ import { LogOut, PanelRight } from "lucide-react";
 import type { ReactNode } from "react";
 import type { GuestSnapshot } from "../../lib/client";
 import { fmtPercent, shortenPath } from "../../lib/format";
+import { ThemeToggle } from "./ThemeToggle";
 
 export interface HeaderBarProps {
 	snapshot: GuestSnapshot;
@@ -69,6 +70,7 @@ export function HeaderBar({ snapshot, subCount, railOpen, onToggleRail, onLeave
 					</span>
 				)}
 				<span className={`sh-dot sh-dot-${phase}`} title={phase} />
+				<ThemeToggle />
 				<button
 					type="button"
 					className={railOpen ? "sh-btn sh-btn-icon sh-btn-on" : "sh-btn sh-btn-icon"}
diff --git a/packages/collab-web/src/components/shell/ThemeToggle.tsx b/packages/collab-web/src/components/shell/ThemeToggle.tsx
new file mode 100644
index 000000000..486625624
--- /dev/null
+++ b/packages/collab-web/src/components/shell/ThemeToggle.tsx
@@ -0,0 +1,37 @@
+import { type LucideIcon, Monitor, Moon, Sun } from "lucide-react";
+import { type ThemePreference, useThemePreference } from "../../lib/theme";
+
+const NEXT_PREFERENCE: Record<ThemePreference, ThemePreference> = {
+	system: "light",
+	light: "dark",
+	dark: "system",
+};
+
+const PREFERENCE_ICON: Record<ThemePreference, LucideIcon> = {
+	system: Monitor,
+	light: Sun,
+	dark: Moon,
+};
+
+const PREFERENCE_LABEL: Record<ThemePreference, string> = {
+	system: "System theme",
+	light: "Light theme",
+	dark: "Dark theme",
+};
+
+export function ThemeToggle() {
+	const { preference, setPreference } = useThemePreference();
+	const Icon = PREFERENCE_ICON[preference];
+
+	return (
+		<button
+			type="button"
+			className="sh-theme-toggle"
+			onClick={() => setPreference(NEXT_PREFERENCE[preference])}
+			aria-label={`${PREFERENCE_LABEL[preference]} (click to switch)`}
+			title={`${PREFERENCE_LABEL[preference]} — click to switch`}
+		>
+			<Icon size={16} />
+		</button>
+	);
+}
diff --git a/packages/collab-web/src/components/shell/shell.css b/packages/collab-web/src/components/shell/shell.css
index 39956019c..084d084d9 100644
--- a/packages/collab-web/src/components/shell/shell.css
+++ b/packages/collab-web/src/components/shell/shell.css
@@ -119,6 +119,33 @@
 	border-color: var(--border-strong);
 }
 
+/* ---- theme toggle (system / light / dark) ---- */
+.sh-theme-toggle {
+	display: inline-flex;
+	align-items: center;
+	justify-content: center;
+	width: 32px;
+	height: 32px;
+	flex-shrink: 0;
+	border: 1px solid var(--border);
+	border-radius: var(--radius);
+	background: var(--bg-raised);
+	color: var(--fg-muted);
+	cursor: pointer;
+	transition: color 0.14s ease, background 0.14s ease, border-color 0.14s ease;
+}
+
+.sh-theme-toggle:hover {
+	color: var(--fg);
+	border-color: var(--border-strong);
+}
+
+@media (prefers-reduced-motion: reduce) {
+	.sh-theme-toggle {
+		transition: none;
+	}
+}
+
 .sh-badge {
 	position: absolute;
 	top: -5px;
@@ -469,8 +496,9 @@
 
 .sh-connect-card {
 	width: 100%;
-	max-width: 360px;
+	max-width: 380px;
 	padding: 28px;
+	position: relative;
 	display: flex;
 	flex-direction: column;
 	gap: 12px;
@@ -479,16 +507,45 @@
 	border-radius: var(--radius-lg);
 }
 
+.sh-connect-head {
+	display: flex;
+	align-items: center;
+	justify-content: space-between;
+	gap: 12px;
+}
+
 .sh-lockup {
+	display: inline-flex;
+	align-items: center;
+	gap: 8px;
 	font: 500 15px / 1.5 var(--font-mono);
 	letter-spacing: 0.02em;
-	margin-bottom: 6px;
+	margin: 0;
+}
+
+.sh-lockup-mark {
+	width: 16px;
+	height: 16px;
+	flex: none;
+	background: linear-gradient(135deg, #ed4abf 0%, #9b4dff 50%, #5ad8e6 100%);
+	border-radius: 4px;
 }
 
 .sh-lockup-pi {
 	color: var(--accent);
 }
 
+.sh-connect-sub {
+	font-size: 12px;
+	color: var(--fg-muted);
+	margin-top: -4px;
+}
+
+.sh-field-hint {
+	font-size: 11px;
+	color: var(--fg-faint);
+}
+
 .sh-field {
 	display: flex;
 	flex-direction: column;
diff --git a/packages/collab-web/src/lib/theme.ts b/packages/collab-web/src/lib/theme.ts
new file mode 100644
index 000000000..0ca8a8de5
--- /dev/null
+++ b/packages/collab-web/src/lib/theme.ts
@@ -0,0 +1,87 @@
+import { useSyncExternalStore } from "react";
+
+export type SystemTheme = "light" | "dark";
+export type ThemePreference = "system" | "light" | "dark";
+
+const STORAGE_KEY = "omp-collab-theme";
+const DARK_SCHEME_QUERY = "(prefers-color-scheme: dark)";
+
+function readStoredPreference(): ThemePreference {
+	if (typeof localStorage === "undefined") return "system";
+	const stored = localStorage.getItem(STORAGE_KEY);
+	return stored === "light" || stored === "dark" || stored === "system" ? stored : "system";
+}
+
+function getSystemTheme(): SystemTheme {
+	if (typeof window === "undefined") return "dark";
+	return window.matchMedia(DARK_SCHEME_QUERY).matches ? "dark" : "light";
+}
+
+// Module-level store shared by the toggle (writer) and any reader so an explicit
+// override and the system default resolve through one source.
+let preference: ThemePreference = readStoredPreference();
+let resolved: SystemTheme = preference === "system" ? getSystemTheme() : preference;
+const listeners = new Set<() => void>();
+
+function emit(): void {
+	for (const listener of listeners) listener();
+}
+
+function applyResolvedTheme(): void {
+	resolved = preference === "system" ? getSystemTheme() : preference;
+	if (typeof document !== "undefined") {
+		document.documentElement.dataset.theme = resolved;
+		document.documentElement.style.colorScheme = resolved;
+	}
+}
+
+if (typeof window !== "undefined") {
+	applyResolvedTheme();
+	window.matchMedia(DARK_SCHEME_QUERY).addEventListener("change", () => {
+		// System changes only move the needle while following the system.
+		if (preference === "system") {
+			applyResolvedTheme();
+			emit();
+		}
+	});
+}
+
+export function setThemePreference(next: ThemePreference): void {
+	preference = next;
+	if (typeof localStorage !== "undefined") localStorage.setItem(STORAGE_KEY, next);
+	applyResolvedTheme();
+	emit();
+}
+
+function subscribe(callback: () => void): () => void {
+	listeners.add(callback);
+	return () => listeners.delete(callback);
+}
+
+/** Reader for the active resolved theme. Reflects system default and overrides. */
+export function useSystemTheme(): SystemTheme {
+	return useSyncExternalStore(
+		subscribe,
+		() => resolved,
+		() => "dark" as SystemTheme,
+	);
+}
+
+/** Reader + writer for the theme preference (powers the toggle). */
+export function useThemePreference(): {
+	preference: ThemePreference;
+	resolved: SystemTheme;
+	setPreference: (next: ThemePreference) => void;
+} {
+	const pref = useSyncExternalStore(
+		subscribe,
+		() => preference,
+		() => "system" as ThemePreference,
+	);
+	const res = useSyncExternalStore(
+		subscribe,
+		() => resolved,
+		() => "dark" as SystemTheme,
+	);
+	return { preference: pref, resolved: res, setPreference: setThemePreference };
+}
diff --git a/packages/collab-web/src/styles/base.css b/packages/collab-web/src/styles/base.css
index e11f86da1..2fc380fd4 100644
--- a/packages/collab-web/src/styles/base.css
+++ b/packages/collab-web/src/styles/base.css
@@ -80,13 +80,21 @@ textarea {
 }
 
 *::-webkit-scrollbar {
-	width: 8px;
-	height: 8px;
+	width: 10px;
+	height: 10px;
 }
 
 *::-webkit-scrollbar-thumb {
 	background: var(--border-strong);
-	border-radius: var(--radius);
+	border: 2px solid transparent;
+	background-clip: padding-box;
+	border-radius: 999px;
+}
+
+*::-webkit-scrollbar-thumb:hover {
+	background: var(--fg-faint);
+	border: 2px solid transparent;
+	background-clip: padding-box;
 }
 
 *::-webkit-scrollbar-track {
diff --git a/packages/collab-web/src/styles/tokens.css b/packages/collab-web/src/styles/tokens.css
index b2a2c03bc..ac96c443c 100644
--- a/packages/collab-web/src/styles/tokens.css
+++ b/packages/collab-web/src/styles/tokens.css
@@ -1,5 +1,6 @@
-/* Design tokens — dark-only devtool aesthetic on the omp brand palette:
- * deep-purple surfaces, pink accent, cyan focus ring.
+/* Design tokens — omp brand palette: deep-purple surfaces, pink accent, cyan
+ * focus ring. Dark is the default; `[data-theme="light"]` and the
+ * prefers-color-scheme light fallback flip to light surfaces.
  * The ONLY file allowed to contain raw color values. */
 :root {
 	color-scheme: dark;
@@ -8,7 +9,7 @@
 	--bg: oklch(0.16 0.02 307);
 	--bg-raised: oklch(0.19 0.022 307);
 	--bg-inset: oklch(0.13 0.016 307);
-	--bg-overlay: oklch(0.22 0.026 307);
+	--bg-overlay: oklch(0.235 0.026 307);
 
 	/* text */
 	--fg: oklch(0.92 0.01 307);
@@ -36,11 +37,71 @@
 	--font-mono: ui-monospace, "SF Mono", "JetBrains Mono", "Cascadia Mono", Menlo, Consolas, monospace;
 
 	/* radii */
-	--radius-sm: 2px;
-	--radius: 4px;
+	--radius-sm: 3px;
+	--radius: 6px;
 	--radius-lg: 8px;
 
 	/* non-pinned helpers (kept here so no raw colors leak outside this file) */
 	--shadow-overlay: 0 12px 32px oklch(0 0 0 / 45%), 0 2px 8px oklch(0 0 0 / 30%);
 	--backdrop: oklch(0.1 0.014 307 / 62%);
 }
+
+/* Light theme — explicit override (toggle writes data-theme="light"). */
+[data-theme="light"] {
+	color-scheme: light;
+
+	--bg: oklch(0.985 0.004 307);
+	--bg-raised: oklch(1 0 0);
+	--bg-inset: oklch(0.95 0.006 307);
+	--bg-overlay: oklch(0.965 0.006 307);
+
+	--fg: oklch(0.26 0.03 307);
+	--fg-muted: oklch(0.46 0.03 307);
+	--fg-faint: oklch(0.58 0.025 307);
+
+	--accent: oklch(0.62 0.23 341);
+	--accent-fg: oklch(0.99 0.01 341);
+	--accent-muted: oklch(0.62 0.23 341 / 14%);
+
+	--ok: oklch(0.55 0.13 150);
+	--warn: oklch(0.6 0.13 85);
+	--err: oklch(0.55 0.19 25);
+
+	--border: oklch(0 0 0 / 10%);
+	--border-strong: oklch(0 0 0 / 15%);
+	--ring: oklch(0.58 0.13 230 / 70%);
+
+	--shadow-overlay: 0 12px 32px oklch(0 0 0 / 14%), 0 2px 8px oklch(0 0 0 / 10%);
+	--backdrop: oklch(0.55 0.02 307 / 28%);
+}
+
+/* Light theme — system fallback when no explicit preference is stored. */
+@media (prefers-color-scheme: light) {
+	:root:not([data-theme]) {
+		color-scheme: light;
+
+		--bg: oklch(0.985 0.004 307);
+		--bg-raised: oklch(1 0 0);
+		--bg-inset: oklch(0.95 0.006 307);
+		--bg-overlay: oklch(0.965 0.006 307);
+
+		--fg: oklch(0.26 0.03 307);
+		--fg-muted: oklch(0.46 0.03 307);
+		--fg-faint: oklch(0.58 0.025 307);
+
+		--accent: oklch(0.62 0.23 341);
+		--accent-fg: oklch(0.99 0.01 341);
+		--accent-muted: oklch(0.62 0.23 341 / 14%);
+
+		--ok: oklch(0.55 0.13 150);
+		--warn: oklch(0.6 0.13 85);
+		--err: oklch(0.55 0.19 25);
+
+		--border: oklch(0 0 0 / 10%);
+		--border-strong: oklch(0 0 0 / 15%);
+		--ring: oklch(0.58 0.13 230 / 70%);
+
+		--shadow-overlay: 0 12px 32px oklch(0 0 0 / 14%), 0 2px 8px oklch(0 0 0 / 10%);
+		--backdrop: oklch(0.55 0.02 307 / 28%);
+	}
+}