diff --git a/public/css/styles.css b/public/css/styles.css
index f8855a2..0374336 100644
--- a/public/css/styles.css
+++ b/public/css/styles.css
@@ -1 +1,319 @@
-/* Mythic Oracle — styles */
+/* Mythic Oracle — design tokens, layout, typography, sidebar */
+
+:root {
+  --font-heading: 'Cormorant Garamond', serif;
+  --font-body: 'Lora', serif;
+  --font-mono: 'JetBrains Mono', monospace;
+
+  --sidebar-width: 220px;
+  --sidebar-width-collapsed: 52px;
+  --transition-speed: 0.2s;
+}
+
+[data-theme="dark"] {
+  --bg: #121110;
+  --bg-elevated: #181613;
+  --bg-hover: #221f1a;
+  --border: #2c2822;
+
+  --text-primary: #e8e2d6;
+  --text-secondary: #b0a795;
+  --text-muted: #756c5c;
+
+  --accent: #c9a35c;
+  --accent-hover: #ddb876;
+  --accent-text: #121110;
+}
+
+[data-theme="light"] {
+  --bg: #f5f1ea;
+  --bg-elevated: #ece4d4;
+  --bg-hover: #e1d6c0;
+  --border: #d6c9ac;
+
+  --text-primary: #2b2620;
+  --text-secondary: #55503f;
+  --text-muted: #8a8168;
+
+  --accent: #a3822f;
+  --accent-hover: #8c6f27;
+  --accent-text: #f5f1ea;
+}
+
+* ,
+*::before,
+*::after {
+  box-sizing: border-box;
+}
+
+html,
+body {
+  height: 100%;
+  margin: 0;
+  padding: 0;
+}
+
+body {
+  font-family: var(--font-body);
+  background: var(--bg);
+  color: var(--text-primary);
+  -webkit-font-smoothing: antialiased;
+}
+
+h1, h2, h3, h4, h5, h6 {
+  font-family: var(--font-heading);
+  font-weight: 600;
+  color: var(--text-primary);
+  margin: 0 0 0.5em;
+}
+
+.app {
+  display: flex;
+  height: 100vh;
+  overflow: hidden;
+}
+
+/* --- Sidebar --- */
+
+.sidebar {
+  display: flex;
+  flex-direction: column;
+  flex-shrink: 0;
+  width: var(--sidebar-width);
+  background: var(--bg-elevated);
+  border-right: 1px solid var(--border);
+  transition: width var(--transition-speed) ease;
+  overflow: hidden;
+}
+
+.sidebar.collapsed {
+  width: var(--sidebar-width-collapsed);
+}
+
+.sidebar-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 8px;
+  padding: 16px;
+  border-bottom: 1px solid var(--border);
+  flex-shrink: 0;
+}
+
+.sidebar-brand {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  overflow: hidden;
+}
+
+.sidebar-logo {
+  flex-shrink: 0;
+  width: 20px;
+  height: 20px;
+  color: var(--accent);
+}
+
+.sidebar-title {
+  font-family: var(--font-heading);
+  font-size: 1.3rem;
+  font-weight: 600;
+  color: var(--accent);
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
+
+.sidebar.collapsed .sidebar-title {
+  display: none;
+}
+
+.sidebar-collapse-toggle {
+  flex-shrink: 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 24px;
+  height: 24px;
+  padding: 0;
+  background: none;
+  border: none;
+  color: var(--text-secondary);
+  cursor: pointer;
+}
+
+.sidebar-collapse-toggle:hover {
+  color: var(--accent);
+}
+
+.sidebar-collapse-toggle svg {
+  width: 16px;
+  height: 16px;
+  transition: transform var(--transition-speed) ease;
+}
+
+.sidebar.collapsed .sidebar-collapse-toggle svg {
+  transform: rotate(180deg);
+}
+
+.sidebar-nav {
+  flex: 1;
+  overflow-y: auto;
+  overflow-x: hidden;
+  padding: 8px 0;
+}
+
+.nav-section {
+  margin-bottom: 12px;
+}
+
+.nav-section-label {
+  padding: 8px 16px 4px;
+  font-family: var(--font-body);
+  font-size: 0.7rem;
+  font-weight: 600;
+  letter-spacing: 0.08em;
+  text-transform: uppercase;
+  color: var(--text-muted);
+  white-space: nowrap;
+}
+
+.sidebar.collapsed .nav-section-label {
+  display: none;
+}
+
+.nav-item {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  width: 100%;
+  padding: 8px 16px;
+  border: none;
+  border-left: 2px solid transparent;
+  background: none;
+  color: var(--text-secondary);
+  font-family: var(--font-body);
+  font-size: 0.9rem;
+  text-align: left;
+  cursor: pointer;
+  transition: background var(--transition-speed) ease, color var(--transition-speed) ease;
+}
+
+.nav-item:hover {
+  background: var(--bg-hover);
+  color: var(--text-primary);
+}
+
+.nav-item.active {
+  background: var(--bg-hover);
+  color: var(--accent);
+  border-left-color: var(--accent);
+}
+
+.nav-icon {
+  flex-shrink: 0;
+  width: 18px;
+  height: 18px;
+}
+
+.nav-label {
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
+
+.sidebar.collapsed .nav-item {
+  justify-content: center;
+  padding: 10px 0;
+  border-left: none;
+  border-right: 2px solid transparent;
+}
+
+.sidebar.collapsed .nav-item.active {
+  border-right-color: var(--accent);
+}
+
+.sidebar.collapsed .nav-label {
+  display: none;
+}
+
+/* --- Chaos factor --- */
+
+.chaos-factor {
+  flex-shrink: 0;
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+  padding: 12px 16px;
+  border-top: 1px solid var(--border);
+}
+
+.chaos-factor-label {
+  font-size: 0.7rem;
+  font-weight: 600;
+  letter-spacing: 0.08em;
+  text-transform: uppercase;
+  color: var(--text-muted);
+  white-space: nowrap;
+}
+
+.sidebar.collapsed .chaos-factor-label {
+  display: none;
+}
+
+.chaos-factor-controls {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 8px;
+}
+
+.sidebar.collapsed .chaos-factor-controls {
+  flex-direction: column-reverse;
+}
+
+.chaos-btn {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  flex-shrink: 0;
+  width: 24px;
+  height: 24px;
+  border: 1px solid var(--border);
+  border-radius: 4px;
+  background: var(--bg);
+  color: var(--text-primary);
+  font-family: var(--font-mono);
+  font-size: 0.9rem;
+  cursor: pointer;
+  transition: border-color var(--transition-speed) ease, color var(--transition-speed) ease;
+}
+
+.chaos-btn:hover {
+  border-color: var(--accent);
+  color: var(--accent);
+}
+
+.chaos-factor-value {
+  min-width: 1.5em;
+  font-family: var(--font-mono);
+  font-size: 1.1rem;
+  color: var(--accent);
+  text-align: center;
+}
+
+/* --- Main content --- */
+
+.main-content {
+  flex: 1;
+  overflow-y: auto;
+  padding: 24px;
+}
+
+.view {
+  display: none;
+}
+
+.view.active {
+  display: block;
+}
diff --git a/public/index.html b/public/index.html
index 81c40ee..bcbf7d5 100644
--- a/public/index.html
+++ b/public/index.html
@@ -12,7 +12,139 @@
   <link rel="stylesheet" href="css/styles.css">
 </head>
 <body>
+  <div class="app">
+    <aside class="sidebar" id="sidebar">
+      <div class="sidebar-header">
+        <div class="sidebar-brand">
+          <svg class="sidebar-logo" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+            <path d="M12 3l1.8 4.6L18 9l-4.2 1.4L12 15l-1.8-4.6L6 9l4.2-1.4L12 3z"/>
+          </svg>
+          <span class="sidebar-title">Mythic Oracle</span>
+        </div>
+        <button class="sidebar-collapse-toggle" id="collapseToggle" aria-label="Collapse sidebar">
+          <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+            <path d="M15 6l-6 6 6 6"/>
+          </svg>
+        </button>
+      </div>
 
+      <nav class="sidebar-nav">
+        <div class="nav-section">
+          <div class="nav-section-label">Oracle</div>
+          <button class="nav-item active" data-view="oracle">
+            <svg class="nav-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+              <circle cx="12" cy="11" r="7"/>
+              <path d="M6 20h12"/>
+            </svg>
+            <span class="nav-label">Oracle</span>
+          </button>
+          <button class="nav-item" data-view="meaning">
+            <svg class="nav-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+              <path d="M4 4h16v12H8l-4 4V4z"/>
+            </svg>
+            <span class="nav-label">Meaning</span>
+          </button>
+          <button class="nav-item" data-view="une">
+            <svg class="nav-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+              <path d="M4 6h16M4 12h16M4 18h10"/>
+            </svg>
+            <span class="nav-label">UNE</span>
+          </button>
+        </div>
+
+        <div class="nav-section">
+          <div class="nav-section-label">Tools</div>
+          <button class="nav-item" data-view="dice">
+            <svg class="nav-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+              <rect x="4" y="4" width="16" height="16" rx="3"/>
+              <circle cx="8.5" cy="8.5" r="0.75" fill="currentColor" stroke="none"/>
+              <circle cx="15.5" cy="8.5" r="0.75" fill="currentColor" stroke="none"/>
+              <circle cx="12" cy="12" r="0.75" fill="currentColor" stroke="none"/>
+              <circle cx="8.5" cy="15.5" r="0.75" fill="currentColor" stroke="none"/>
+              <circle cx="15.5" cy="15.5" r="0.75" fill="currentColor" stroke="none"/>
+            </svg>
+            <span class="nav-label">Dice</span>
+          </button>
+          <button class="nav-item" data-view="tables">
+            <svg class="nav-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+              <rect x="3" y="3" width="18" height="18" rx="1"/>
+              <path d="M3 9h18M3 15h18M9 3v18M15 3v18"/>
+            </svg>
+            <span class="nav-label">Tables</span>
+          </button>
+        </div>
+
+        <div class="nav-section">
+          <div class="nav-section-label">Campaign</div>
+          <button class="nav-item" data-view="threads">
+            <svg class="nav-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+              <path d="M4 6h2M4 12h2M4 18h2M9 6h11M9 12h11M9 18h11"/>
+            </svg>
+            <span class="nav-label">Threads</span>
+          </button>
+          <button class="nav-item" data-view="npcs">
+            <svg class="nav-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+              <circle cx="12" cy="8" r="4"/>
+              <path d="M4 20c0-4 4-6 8-6s8 2 8 6"/>
+            </svg>
+            <span class="nav-label">NPCs</span>
+          </button>
+          <button class="nav-item" data-view="notes">
+            <svg class="nav-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+              <path d="M6 3h9l3 3v15H6z"/>
+              <path d="M9 8h8M9 12h8M9 16h5"/>
+            </svg>
+            <span class="nav-label">Notes</span>
+          </button>
+          <button class="nav-item" data-view="character">
+            <svg class="nav-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+              <path d="M12 3l7 3v6c0 5-3.5 8-7 9-3.5-1-7-4-7-9V6z"/>
+            </svg>
+            <span class="nav-label">Character</span>
+          </button>
+        </div>
+
+        <div class="nav-section">
+          <div class="nav-section-label">Settings</div>
+          <button class="nav-item" data-view="campaign-management">
+            <svg class="nav-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+              <circle cx="12" cy="12" r="3"/>
+              <path d="M12 2v3M12 19v3M4.2 4.2l2.1 2.1M17.7 17.7l2.1 2.1M2 12h3M19 12h3M4.2 19.8l2.1-2.1M17.7 6.3l2.1-2.1"/>
+            </svg>
+            <span class="nav-label">Campaign Management</span>
+          </button>
+          <button class="nav-item nav-action" id="themeToggle" aria-label="Toggle light and dark theme">
+            <svg class="nav-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">
+              <path d="M20 14.5A8.5 8.5 0 1 1 9.5 4a7 7 0 0 0 10.5 10.5z"/>
+            </svg>
+            <span class="nav-label">Theme Toggle</span>
+          </button>
+        </div>
+      </nav>
+
+      <div class="chaos-factor">
+        <div class="chaos-factor-label">Chaos Factor</div>
+        <div class="chaos-factor-controls">
+          <button class="chaos-btn" id="chaosMinus" aria-label="Decrease chaos factor">&minus;</button>
+          <span class="chaos-factor-value" id="chaosValue">5</span>
+          <button class="chaos-btn" id="chaosPlus" aria-label="Increase chaos factor">+</button>
+        </div>
+      </div>
+    </aside>
+
+    <main class="main-content">
+      <div class="view active" id="view-oracle"></div>
+      <div class="view" id="view-meaning"></div>
+      <div class="view" id="view-une"></div>
+      <div class="view" id="view-dice"></div>
+      <div class="view" id="view-tables"></div>
+      <div class="view" id="view-threads"></div>
+      <div class="view" id="view-npcs"></div>
+      <div class="view" id="view-notes"></div>
+      <div class="view" id="view-character"></div>
+      <div class="view" id="view-campaign-management"></div>
+    </main>
+  </div>
 </body>
 <script src="js/app.js" type="module"></script>
 </html>
diff --git a/public/js/app.js b/public/js/app.js
index 6968a7d..d7e1ccc 100644
--- a/public/js/app.js
+++ b/public/js/app.js
@@ -1 +1,85 @@
 // Mythic Oracle — entry, sidebar routing, campaign context
+
+const STORAGE_KEYS = {
+  sidebarCollapsed: 'mo-sidebar-collapsed',
+  activeView: 'mo-active-view',
+  theme: 'mo-theme',
+};
+
+const CHAOS_MIN = 1;
+const CHAOS_MAX = 9;
+
+function initSidebarCollapse() {
+  const sidebar = document.getElementById('sidebar');
+  const toggle = document.getElementById('collapseToggle');
+
+  const collapsed = localStorage.getItem(STORAGE_KEYS.sidebarCollapsed) === 'true';
+  sidebar.classList.toggle('collapsed', collapsed);
+
+  toggle.addEventListener('click', () => {
+    const isCollapsed = sidebar.classList.toggle('collapsed');
+    localStorage.setItem(STORAGE_KEYS.sidebarCollapsed, isCollapsed);
+  });
+}
+
+function initNavRouting() {
+  const navItems = document.querySelectorAll('.nav-item[data-view]');
+  const views = document.querySelectorAll('.view');
+
+  function activateView(viewId) {
+    navItems.forEach((item) => {
+      item.classList.toggle('active', item.dataset.view === viewId);
+    });
+    views.forEach((view) => {
+      view.classList.toggle('active', view.id === `view-${viewId}`);
+    });
+  }
+
+  navItems.forEach((item) => {
+    item.addEventListener('click', () => {
+      const viewId = item.dataset.view;
+      activateView(viewId);
+      localStorage.setItem(STORAGE_KEYS.activeView, viewId);
+    });
+  });
+
+  const savedView = localStorage.getItem(STORAGE_KEYS.activeView);
+  const validView = savedView && document.getElementById(`view-${savedView}`);
+  activateView(validView ? savedView : 'oracle');
+}
+
+function initThemeToggle() {
+  const toggle = document.getElementById('themeToggle');
+  const root = document.documentElement;
+
+  const savedTheme = localStorage.getItem(STORAGE_KEYS.theme) || 'dark';
+  root.setAttribute('data-theme', savedTheme);
+
+  toggle.addEventListener('click', () => {
+    const nextTheme = root.getAttribute('data-theme') === 'dark' ? 'light' : 'dark';
+    root.setAttribute('data-theme', nextTheme);
+    localStorage.setItem(STORAGE_KEYS.theme, nextTheme);
+  });
+}
+
+function initChaosFactorControls() {
+  const value = document.getElementById('chaosValue');
+  const minus = document.getElementById('chaosMinus');
+  const plus = document.getElementById('chaosPlus');
+
+  function setValue(next) {
+    value.textContent = Math.min(CHAOS_MAX, Math.max(CHAOS_MIN, next));
+  }
+
+  minus.addEventListener('click', () => setValue(Number(value.textContent) - 1));
+  plus.addEventListener('click', () => setValue(Number(value.textContent) + 1));
+}
+
+function init() {
+  initSidebarCollapse();
+  initNavRouting();
+  initThemeToggle();
+  initChaosFactorControls();
+}
+
+document.addEventListener('DOMContentLoaded', init);