feat: Implement a dark theme and modern UI components with improved layout and styling.

frontend/src/App.css

@@ -2,41 +2,79 @@
   max-width: 1280px;
   margin: 0 auto;
   padding: 2rem;
-  text-align: center;
-}
-
-.logo {
-  height: 6em;
-  padding: 1.5em;
-  will-change: filter;
-  transition: filter 300ms;
-}
-.logo:hover {
-  filter: drop-shadow(0 0 2em #646cffaa);
-}
-.logo.react:hover {
-  filter: drop-shadow(0 0 2em #61dafbaa);
-}
-
-@keyframes logo-spin {
-  from {
-    transform: rotate(0deg);
-  }
-  to {
-    transform: rotate(360deg);
-  }
-}
-
-@media (prefers-reduced-motion: no-preference) {
-  a:nth-of-type(2) .logo {
-    animation: logo-spin infinite 20s linear;
-  }
+  width: 100%;
 }
 
 .card {
-  padding: 2em;
+  background-color: var(--secondary-bg);
+  padding: 2rem;
+  border-radius: 16px;
+  box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
+  border: 1px solid var(--border-color);
 }
 
-.read-the-docs {
-  color: #888;
+.navbar {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  margin-bottom: 2rem;
+  padding-bottom: 1rem;
+  border-bottom: 1px solid var(--border-color);
+}
+
+.nav-links {
+  display: flex;
+  gap: 1.5rem;
+}
+
+.nav-link {
+  font-size: 1.2rem;
+  font-weight: 600;
+  color: var(--text-muted);
+  transition: color 0.2s;
+}
+
+.nav-link:hover, .nav-link.active {
+  color: var(--accent-color);
+}
+
+.form-group {
+  display: flex;
+  flex-direction: column;
+  gap: 0.5rem;
+  margin-bottom: 1rem;
+}
+
+.form-group label {
+  font-size: 0.9rem;
+  color: var(--text-muted);
+}
+
+.btn-secondary {
+  background-color: var(--secondary-alt-bg);
+  border: 1px solid var(--border-color);
+}
+
+.btn-secondary:hover {
+  background-color: var(--border-color);
+}
+
+.list-item {
+  background-color: var(--secondary-alt-bg);
+  padding: 1rem;
+  border-radius: 8px;
+  margin-bottom: 1rem;
+  border: 1px solid var(--border-color);
+  transition: transform 0.2s;
+}
+
+.list-item:hover {
+  transform: translateY(-2px);
+  border-color: var(--accent-color);
+}
+
+.grid-container {
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
+  gap: 1.5rem;
 }