diff --git a/apps/web/src/lib/styles/base.css b/apps/web/src/lib/styles/base.css
new file mode 100644
index 0000000..5481929
--- /dev/null
+++ b/apps/web/src/lib/styles/base.css
@@ -0,0 +1,63 @@
+/* Reset/normalización ligera */
+*,
+*::before,
+*::after { box-sizing: border-box; }
+html, body { height: 100%; }
+body {
+  margin: 0;
+  font-family: ui-sans-serif, system-ui, -apple-system, Segoe UI, Roboto, Noto Sans, Ubuntu, Cantarell, Helvetica Neue, Arial, "Apple Color Emoji", "Segoe UI Emoji";
+  font-size: 16px;
+  line-height: 1.5;
+  background: var(--color-bg);
+  color: var(--color-text);
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+}
+img, svg, video { display: block; max-width: 100%; }
+a { color: inherit; text-decoration: none; }
+button { font: inherit; }
+
+/* Accesibilidad: foco visible */
+:focus-visible {
+  outline: 2px solid var(--color-primary);
+  outline-offset: 2px;
+}
+
+/* Utilidades */
+.container {
+  max-width: 960px;
+  margin: 0 auto;
+  padding: 0 var(--space-4);
+}
+
+.sr-only {
+  position: absolute !important;
+  width: 1px; height: 1px;
+  padding: 0; margin: -1px;
+  overflow: hidden; clip: rect(0,0,0,0);
+  white-space: nowrap; border: 0;
+}
+
+/* Controles base */
+button,
+input[type="submit"] {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  min-height: 44px;
+  padding: 0 12px;
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius-sm);
+  background: var(--color-surface);
+  color: var(--color-text);
+  cursor: pointer;
+}
+button.primary {
+  background: var(--color-primary);
+  border-color: var(--color-primary);
+  color: white;
+}
+button:disabled {
+  opacity: 0.6;
+  cursor: not-allowed;
+}
diff --git a/apps/web/src/lib/styles/tokens.css b/apps/web/src/lib/styles/tokens.css
new file mode 100644
index 0000000..07209a8
--- /dev/null
+++ b/apps/web/src/lib/styles/tokens.css
@@ -0,0 +1,39 @@
+:root {
+  --color-bg: #ffffff;
+  --color-surface: #f7f7f8;
+  --color-text: #111111;
+  --color-text-muted: #555555;
+  --color-border: #e5e7eb;
+
+  --color-primary: #2563eb; /* azul */
+  --color-danger: #dc2626;  /* rojo */
+  --color-warning: #d97706; /* ámbar */
+  --color-success: #16a34a; /* verde */
+
+  --radius-sm: 6px;
+  --radius-md: 8px;
+
+  --shadow-sm: 0 1px 2px rgba(0,0,0,0.06);
+  --shadow-md: 0 4px 12px rgba(0,0,0,0.08);
+
+  --space-1: 4px;
+  --space-2: 8px;
+  --space-3: 12px;
+  --space-4: 16px;
+  --space-5: 24px;
+}
+
+@media (prefers-color-scheme: dark) {
+  :root {
+    --color-bg: #0b0c0f;
+    --color-surface: #14161a;
+    --color-text: #e6e7eb;
+    --color-text-muted: #a1a1aa;
+    --color-border: #26272b;
+
+    --color-primary: #60a5fa;
+    --color-danger: #f87171;
+    --color-warning: #fbbf24;
+    --color-success: #34d399;
+  }
+}
diff --git a/apps/web/src/lib/ui/layout/AppShell.svelte b/apps/web/src/lib/ui/layout/AppShell.svelte
new file mode 100644
index 0000000..d1e38ae
--- /dev/null
+++ b/apps/web/src/lib/ui/layout/AppShell.svelte
@@ -0,0 +1,70 @@
+<script lang="ts">
+  let { children } = $props();
+</script>
+
+<header class="app-header">
+  <div class="container row">
+    <a class="brand" href="/app" aria-label="Inicio">Tareas</a>
+    <nav class="nav">
+      <a href="/app">Mis tareas</a>
+      <a href="/app/groups">Grupos</a>
+      <a href="/app/preferences">Preferencias</a>
+    </nav>
+    <form method="POST" action="/api/logout">
+      <button type="submit" class="logout">Cerrar sesión</button>
+    </form>
+  </div>
+</header>
+
+<main class="container main">
+  {@render children?.()}
+</main>
+
+<style>
+  .app-header {
+    position: sticky;
+    top: 0;
+    z-index: 10;
+    background: var(--color-surface);
+    border-bottom: 1px solid var(--color-border);
+    box-shadow: var(--shadow-sm);
+  }
+  .row {
+    display: flex;
+    align-items: center;
+    gap: var(--space-4);
+    min-height: 56px;
+  }
+  .brand {
+    font-weight: 700;
+    color: var(--color-primary);
+  }
+  .nav {
+    display: flex;
+    gap: var(--space-3);
+    margin-left: auto;
+  }
+  .nav a {
+    padding: 8px 10px;
+    border-radius: var(--radius-sm);
+  }
+  .nav a:hover,
+  .nav a:focus-visible {
+    background: rgba(0,0,0,0.04);
+  }
+  @media (prefers-color-scheme: dark) {
+    .nav a:hover,
+    .nav a:focus-visible {
+      background: rgba(255,255,255,0.06);
+    }
+  }
+  .logout {
+    margin-left: var(--space-3);
+    min-height: 36px;
+    padding: 0 10px;
+  }
+  .main {
+    padding-top: var(--space-5);
+    padding-bottom: var(--space-5);
+  }
+</style>
diff --git a/apps/web/src/routes/+layout.svelte b/apps/web/src/routes/+layout.svelte
index 20f8d04..f4b1d6d 100644
--- a/apps/web/src/routes/+layout.svelte
+++ b/apps/web/src/routes/+layout.svelte
@@ -1,11 +1,14 @@
 <script lang="ts">
 	import favicon from '$lib/assets/favicon.svg';
+	import '$lib/styles/tokens.css';
+	import '$lib/styles/base.css';
 
 	let { children } = $props();
 </script>
 
 <svelte:head>
 	<link rel="icon" href={favicon} />
+	<meta name="robots" content="noindex,nofollow" />
 </svelte:head>
 
 {@render children?.()}
diff --git a/apps/web/src/routes/app/+layout.server.ts b/apps/web/src/routes/app/+layout.server.ts
index 7164642..79628c5 100644
--- a/apps/web/src/routes/app/+layout.server.ts
+++ b/apps/web/src/routes/app/+layout.server.ts
@@ -4,7 +4,7 @@ import { redirect } from '@sveltejs/kit';
 export const load: LayoutServerLoad = async (event) => {
 	const userId = event.locals.userId ?? null;
 	if (!userId) {
-		throw redirect(303, '/');
+		throw redirect(303, '/login');
 	}
 	return { userId };
 };
diff --git a/apps/web/src/routes/app/+layout.svelte b/apps/web/src/routes/app/+layout.svelte
new file mode 100644
index 0000000..87f6323
--- /dev/null
+++ b/apps/web/src/routes/app/+layout.svelte
@@ -0,0 +1,8 @@
+<script lang="ts">
+  import AppShell from '$lib/ui/layout/AppShell.svelte';
+  let { children } = $props();
+</script>
+
+<AppShell>
+  {@render children?.()}
+</AppShell>