diff --git a/content/content.js b/content/content.js
index ea3f828..6192352 100644
--- a/content/content.js
+++ b/content/content.js
@@ -1,7 +1,45 @@
 // Outlook Relook — Content Script Entry Point
-// Loaded by manifest on outlook.office.com/*
 
 (function () {
   'use strict';
-  console.log('[Outlook Relook] Content script loaded');
+
+  const OR = window.OutlookRelook;
+
+  async function init() {
+    const settings = await OR.loadSettings();
+    console.log('[Outlook Relook] Loaded settings:', settings);
+
+    // Apply color scheme attribute
+    applyColorScheme(settings.colorScheme);
+
+    // Listen for setting changes from popup
+    chrome.storage.onChanged.addListener((changes, area) => {
+      if (area !== 'sync') return;
+      console.log('[Outlook Relook] Settings changed:', changes);
+
+      // Re-apply color scheme if it changed
+      if (changes.colorScheme) {
+        applyColorScheme(changes.colorScheme.newValue);
+      }
+    });
+  }
+
+  function applyColorScheme(scheme) {
+    let resolved = scheme;
+    if (scheme === 'system') {
+      resolved = window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
+    }
+    document.documentElement.setAttribute('data-outlook-relook-scheme', resolved);
+    console.log('[Outlook Relook] Color scheme:', resolved);
+  }
+
+  // Listen for system theme changes when scheme is 'system'
+  window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', async () => {
+    const settings = await OR.loadSettings();
+    if (settings.colorScheme === 'system') {
+      applyColorScheme('system');
+    }
+  });
+
+  init();
 })();
diff --git a/content/settings-defaults.js b/content/settings-defaults.js
index 00160d2..4ff846d 100644
--- a/content/settings-defaults.js
+++ b/content/settings-defaults.js
@@ -1 +1,111 @@
-// Outlook Relook — settings-defaults.js (stub, implemented in later task)
+// Outlook Relook — Settings Defaults
+// Loaded first by manifest. Exposes window.OutlookRelook.DEFAULTS and helpers.
+
+window.OutlookRelook = window.OutlookRelook || {};
+
+window.OutlookRelook.DEFAULTS = {
+  // Theme & Appearance
+  theme: 'swiss',
+  colorScheme: 'system',    // 'light' | 'dark' | 'system'
+  accentColor: '',          // empty = theme default
+
+  // Density & Spacing
+  densityPreset: 'compact', // 'comfortable' | 'compact' | 'ultra-compact'
+  compactTopBar: true,
+  compactCommandBar: true,
+  compactMessageList: true,
+  compactReadingPane: true,
+  compactFolderPane: true,
+  narrowDateColumn: true,
+  compressComposeToolbar: true,
+  readingPaneMaxWidth: true,
+
+  // Hide Elements
+  hideCopilot: true,
+  hideSuggestedReplies: true,
+  hidePromoBanners: true,
+  hideFocusedOtherTabs: true,
+  hideSidebarAppIcons: false,
+  hideGroupsSection: false,
+  hideMyDayButtons: true,
+  hideSenderAvatars: false,
+  hideFeatureDiscovery: true,
+  hideVivaInsights: true,
+  hideUnreadOtherBanner: true,
+  hideActivityFeed: true,
+
+  // Readability
+  unreadDistinction: true,
+  previewOwnLine: false,
+  normalizeFontWeight: true,
+  darkModeEmailFix: true,
+  messageListFontSize: 'medium', // 'small' | 'medium' | 'large'
+
+  // Behavior
+  autoCollapseRibbon: true,
+  rememberSidebarState: true,
+  suppressContactHover: true,
+  autoAdvanceAfterDelete: true,
+  autoDismissToasts: '5',   // 'off' | '3' | '5' | '10' (seconds)
+  toastPosition: 'top-right', // 'bottom-left' | 'top-right'
+  stickyReplyBar: true,
+  autoResizeCompose: true,
+  throttleNotifications: false,
+
+  // Keyboard Navigation
+  keyboardMultiSelect: true,
+
+  // Quick Actions
+  markAllReadButton: true,
+  quickFolderJump: true,
+};
+
+// Density presets define which individual toggles each preset sets
+window.OutlookRelook.DENSITY_PRESETS = {
+  comfortable: {
+    compactTopBar: false,
+    compactCommandBar: false,
+    compactMessageList: false,
+    compactReadingPane: false,
+    compactFolderPane: false,
+    narrowDateColumn: false,
+    compressComposeToolbar: false,
+    readingPaneMaxWidth: true,
+  },
+  compact: {
+    compactTopBar: true,
+    compactCommandBar: true,
+    compactMessageList: true,
+    compactReadingPane: true,
+    compactFolderPane: true,
+    narrowDateColumn: true,
+    compressComposeToolbar: true,
+    readingPaneMaxWidth: true,
+  },
+  'ultra-compact': {
+    compactTopBar: true,
+    compactCommandBar: true,
+    compactMessageList: true,
+    compactReadingPane: true,
+    compactFolderPane: true,
+    narrowDateColumn: true,
+    compressComposeToolbar: true,
+    readingPaneMaxWidth: true,
+  },
+};
+
+// Load settings from chrome.storage.sync, filling in defaults for missing keys
+window.OutlookRelook.loadSettings = function () {
+  return new Promise((resolve) => {
+    chrome.storage.sync.get(window.OutlookRelook.DEFAULTS, (settings) => {
+      resolve(settings);
+    });
+  });
+};
+
+// Save a partial settings object to chrome.storage.sync
+window.OutlookRelook.saveSettings = function (partial) {
+  return new Promise((resolve) => {
+    chrome.storage.sync.set(partial, resolve);
+  });
+};