diff --git a/frontend/src/lib/types.ts b/frontend/src/lib/types.ts
index 0d44331..f64bd77 100644
--- a/frontend/src/lib/types.ts
+++ b/frontend/src/lib/types.ts
@@ -1,4 +1,4 @@
-export type Theme = 'light' | 'dark' | 'glass' | 'neon' | 'impeccable' | 'impeccable-dark';
+export type Theme = 'light' | 'dark' | 'glass' | 'neon' | 'impeccable' | 'impeccable-dark' | 'cosmic';
 
 /** Lifecycle of the NIP-46 remote signer. */
 export type SignerPhase = 'stopped' | 'connecting' | 'connected';
diff --git a/frontend/src/screens/SettingsScreen.tsx b/frontend/src/screens/SettingsScreen.tsx
index c8b402d..db2a0d8 100644
--- a/frontend/src/screens/SettingsScreen.tsx
+++ b/frontend/src/screens/SettingsScreen.tsx
@@ -108,6 +108,7 @@ export function SettingsScreen() {
                 <option value="neon">Neon</option>
                 <option value="impeccable">Impeccable — Light</option>
                 <option value="impeccable-dark">Impeccable — Dark</option>
+                <option value="cosmic">Cosmic — Stardust</option>
               </select>
               <div
                 aria-hidden="true"
@@ -179,12 +180,14 @@ export function SettingsScreen() {
                           ? 'Aurora — frosted glass, cyan'
                           : settings.theme === 'dark'
                             ? 'Dark — deep ink'
-                            : 'Light — warm paper'}
+                            : settings.theme === 'cosmic'
+                              ? 'Cosmic — deep space, golden stardust'
+                              : 'Light — warm paper'}
                 </span>
               </div>
               <p className="hint">
-                “Light” and “Dark” follow your manual selection. “Aurora”, “Neon”, “Impeccable” and
-                “Impeccable Dark” are aesthetic themes with distinctive color palettes.
+                "Light" and "Dark" follow your manual selection. "Aurora", "Neon", "Impeccable",
+                "Impeccable Dark", and "Cosmic" are aesthetic themes with distinctive color palettes.
               </p>
             </div>
           </div>
diff --git a/frontend/src/styles.css b/frontend/src/styles.css
index fc7d2fe..6037e1b 100644
--- a/frontend/src/styles.css
+++ b/frontend/src/styles.css
@@ -348,6 +348,230 @@ html[data-theme='impeccable-dark'] .sidebar {
   border-right-color: var(--border);
 }
 
+/* "Cosmic" — Stardust color scheme from https://github.com/kaymade/cosmic
+   Deep space backgrounds with warm golden accents.
+   Fonts: Source Serif 4 for body, Cormorant Garamond for headings.
+   Sidebar: Deep (darker background). Workspace: Deep Space (dramatic vignette). */
+
+@import url('https://fonts.googleapis.com/css2?family=Cormorant+Garamond:ital,wght@0,400;0,500;0,600;0,700;1,400;1,500;1,600;1,700&family=Source+Serif+4:ital,opsz,wght@0,8..60,400;0,8..60,500;0,8..60,600;0,8..60,700;1,8..60,400;1,8..60,500;1,8..60,600;1,8..60,700&display=swap');
+
+:root[data-theme='cosmic'] {
+  /* Stardust dark mode colors */
+  --bg: #171109;
+  --surface: #0d0a06;
+  --surface-2: #21180c;
+  --surface-hover: #140f08;
+  --border: #2d2418;
+  --border-strong: #3d3220;
+  --text: #fff5dc;
+  --text-muted: #d5bd8d;
+  --primary: #efbd62;
+  --primary-hover: #ffdb91;
+  --primary-soft: rgba(239, 189, 98, 0.15);
+  --on-primary: #171109;
+  --danger: #f08e7d;
+  --danger-soft: rgba(240, 142, 125, 0.15);
+  --warning: #f08e7d;
+  --warning-soft: rgba(240, 142, 125, 0.15);
+  --success: #74d7cb;
+  --success-soft: rgba(116, 215, 203, 0.15);
+  --info: #74d7cb;
+  --info-soft: rgba(116, 215, 203, 0.15);
+  --focus: #efbd62;
+  --shadow: 0 2px 8px rgba(0, 0, 0, 0.4);
+  --shadow-modal: 0 12px 40px rgba(0, 0, 0, 0.6);
+  --radius: 8px;
+  --radius-sm: 4px;
+  color-scheme: dark;
+}
+
+/* Cosmic typography - Cormorant Garamond for headings, Source Serif 4 for body */
+html[data-theme='cosmic'] body {
+  font-family: 'Source Serif 4', 'Georgia', serif;
+  font-size: 15px;
+  line-height: 1.6;
+}
+
+html[data-theme='cosmic'] h1,
+html[data-theme='cosmic'] h2,
+html[data-theme='cosmic'] h3,
+html[data-theme='cosmic'] h4 {
+  font-family: 'Cormorant Garamond', 'Georgia', serif;
+  font-weight: 600;
+  letter-spacing: 0.02em;
+}
+
+html[data-theme='cosmic'] h1 {
+  font-size: 28px;
+  color: #efbd62;
+}
+
+html[data-theme='cosmic'] h2 {
+  font-size: 20px;
+  color: #74d7cb;
+}
+
+html[data-theme='cosmic'] h3 {
+  font-size: 18px;
+  color: #f08e7d;
+}
+
+/* Cosmic sidebar - Deep background (darker) */
+html[data-theme='cosmic'] .sidebar {
+  background: #0d0a06;
+  border-right-color: var(--border);
+}
+
+/* Cosmic workspace - Deep Space background with vignette effect */
+html[data-theme='cosmic'] .app-shell {
+  background:
+    radial-gradient(circle at 8% 13%, rgba(255, 245, 220, 0.72) 0 1px, transparent 1.7px),
+    radial-gradient(circle at 27% 7%, rgba(116, 215, 203, 0.82) 0 1px, transparent 1.8px),
+    radial-gradient(circle at 73% 19%, rgba(255, 245, 220, 0.68) 0 1.2px, transparent 1.9px),
+    radial-gradient(circle at 91% 42%, rgba(240, 142, 125, 0.78) 0 1px, transparent 1.8px),
+    radial-gradient(circle at 61% 78%, rgba(255, 245, 220, 0.64) 0 1px, transparent 1.7px),
+    radial-gradient(circle at 18% 84%, rgba(239, 189, 98, 0.82) 0 1.2px, transparent 2px),
+    radial-gradient(circle at 12% 4%, rgba(239, 189, 98, 0.52), transparent 58rem),
+    radial-gradient(circle at 88% 12%, rgba(116, 215, 203, 0.42), transparent 46rem),
+    radial-gradient(circle at 52% 100%, rgba(240, 142, 125, 0.36), transparent 50rem),
+    radial-gradient(ellipse at center, transparent 34%, rgba(13, 10, 6, 0.48) 100%),
+    linear-gradient(145deg, #171109, #0d0a06);
+}
+
+html[data-theme='cosmic'] .main {
+  background: transparent;
+}
+
+/* Cosmic cards and surfaces */
+html[data-theme='cosmic'] .card,
+html[data-theme='cosmic'] .profile-card,
+html[data-theme='cosmic'] .relay-row {
+  background: var(--surface);
+  border-color: var(--border);
+  box-shadow: var(--shadow);
+}
+
+html[data-theme='cosmic'] .card:hover,
+html[data-theme='cosmic'] .profile-card:hover {
+  border-color: var(--primary);
+}
+
+/* Cosmic buttons */
+html[data-theme='cosmic'] .btn-primary {
+  background: var(--primary);
+  color: var(--on-primary);
+}
+
+html[data-theme='cosmic'] .btn-primary:hover:not(:disabled) {
+  background: var(--primary-hover);
+}
+
+html[data-theme='cosmic'] .btn-secondary {
+  background: var(--surface);
+  border-color: var(--border-strong);
+  color: var(--text);
+}
+
+html[data-theme='cosmic'] .btn-ghost {
+  color: var(--text-muted);
+}
+
+html[data-theme='cosmic'] .btn-ghost:hover {
+  background: var(--surface-2);
+  color: var(--text);
+}
+
+/* Cosmic navigation */
+html[data-theme='cosmic'] .nav-item {
+  color: var(--text-muted);
+}
+
+html[data-theme='cosmic'] .nav-item:hover {
+  background: var(--surface-2);
+  color: var(--text);
+}
+
+html[data-theme='cosmic'] .nav-item.is-active {
+  background: var(--primary-soft);
+  color: var(--primary);
+}
+
+/* Cosmic inputs */
+html[data-theme='cosmic'] input[type='text'],
+html[data-theme='cosmic'] input[type='search'],
+html[data-theme='cosmic'] input[type='password'],
+html[data-theme='cosmic'] select,
+html[data-theme='cosmic'] textarea {
+  background: var(--surface);
+  border-color: var(--border-strong);
+  color: var(--text);
+}
+
+html[data-theme='cosmic'] input:focus,
+html[data-theme='cosmic'] select:focus,
+html[data-theme='cosmic'] textarea:focus {
+  border-color: var(--focus);
+  box-shadow: 0 0 0 2px var(--primary-soft);
+}
+
+/* Cosmic code blocks */
+html[data-theme='cosmic'] code,
+html[data-theme='cosmic'] .mono {
+  background: var(--surface-2);
+  border-color: var(--border);
+  color: var(--primary);
+}
+
+/* Cosmic badges */
+html[data-theme='cosmic'] .badge {
+  border-radius: 4px;
+  font-size: 11px;
+  font-weight: 600;
+}
+
+html[data-theme='cosmic'] .badge-neutral {
+  background: var(--surface-2);
+  color: var(--text-muted);
+  border-color: var(--border);
+}
+
+html[data-theme='cosmic'] .badge-success {
+  background: var(--success-soft);
+  color: var(--success);
+}
+
+html[data-theme='cosmic'] .badge-warning {
+  background: var(--warning-soft);
+  color: var(--warning);
+}
+
+html[data-theme='cosmic'] .badge-danger {
+  background: var(--danger-soft);
+  color: var(--danger);
+}
+
+html[data-theme='cosmic'] .badge-info {
+  background: var(--info-soft);
+  color: var(--info);
+}
+
+/* Cosmic modal */
+html[data-theme='cosmic'] .modal {
+  background: var(--surface);
+  border-color: var(--border);
+  box-shadow: var(--shadow-modal);
+}
+
+html[data-theme='cosmic'] .modal-backdrop {
+  background: rgba(13, 10, 6, 0.8);
+}
+
+/* Cosmic empty state */
+html[data-theme='cosmic'] .empty-state {
+  background: var(--surface);
+  border-color: var(--border);
+}
+
 * {
   box-sizing: border-box;
 }
@@ -1944,3 +2168,97 @@ select {
   align-items: flex-start;
   gap: 12px;
 }
+
+/* -------------------------------------------------------------------------
+   Motion system
+   Purposeful motion for feedback, state, and continuity.
+   ------------------------------------------------------------------------- */
+
+@keyframes modal-enter {
+  from {
+    opacity: 0;
+    transform: scale(0.96) translateY(8px);
+  }
+  to {
+    opacity: 1;
+    transform: scale(1) translateY(0);
+  }
+}
+
+@keyframes modal-backdrop-enter {
+  from {
+    opacity: 0;
+  }
+  to {
+    opacity: 1;
+  }
+}
+
+@keyframes alert-enter {
+  from {
+    opacity: 0;
+    transform: translateY(-6px);
+  }
+  to {
+    opacity: 1;
+    transform: translateY(0);
+  }
+}
+
+@keyframes undo-enter {
+  from {
+    opacity: 0;
+    transform: translateY(10px);
+  }
+  to {
+    opacity: 1;
+    transform: translateY(0);
+  }
+}
+
+.modal-backdrop {
+  animation: modal-backdrop-enter 200ms cubic-bezier(0.16, 1, 0.3, 1);
+}
+
+.modal {
+  animation: modal-enter 220ms cubic-bezier(0.16, 1, 0.3, 1);
+}
+
+.alert {
+  animation: alert-enter 200ms cubic-bezier(0.16, 1, 0.3, 1);
+}
+
+.undo-bar {
+  animation: undo-enter 250ms cubic-bezier(0.16, 1, 0.3, 1);
+}
+
+.btn:active:not(:disabled) {
+  transform: scale(0.97);
+  transition: transform 80ms ease;
+}
+
+.profile-card:active:not(.is-active) {
+  transform: scale(0.985);
+  transition: transform 100ms ease;
+}
+
+.nav-item:active {
+  transform: scale(0.98);
+  transition: transform 80ms ease;
+}
+
+@media (prefers-reduced-motion: reduce) {
+  .modal-backdrop,
+  .modal,
+  .alert,
+  .undo-bar {
+    animation: none;
+  }
+
+  .btn:active:not(:disabled),
+  .profile-card:active:not(.is-active),
+  .nav-item:active {
+    transform: none;
+    transition: none;
+  }
+}
diff --git a/src/settings.rs b/src/settings.rs
index c475df6..d4eb9d3 100644
--- a/src/settings.rs
+++ b/src/settings.rs
@@ -27,6 +27,7 @@ pub enum Theme {
     Impeccable,
     #[serde(rename = "impeccable-dark")]
     ImpeccableDark,
+    Cosmic,
 }
 
 impl Theme {
@@ -39,6 +40,7 @@ impl Theme {
             "neon" => Some(Self::Neon),
             "impeccable" => Some(Self::Impeccable),
             "impeccable-dark" => Some(Self::ImpeccableDark),
+            "cosmic" => Some(Self::Cosmic),
             _ => None,
         }
     }