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

frontend/src/index.css

@@ -1,11 +1,20 @@
 :root {
-  font-family: system-ui, Avenir, Helvetica, Arial, sans-serif;
-  line-height: 1.5;
+  --primary-bg: #23283d;
+  --secondary-bg: #1e2233;
+  --secondary-alt-bg: #191f2e;
+  --tertiary-bg: #101320;
+  --accent-color: #096dc0;
+  --text-color: #ffffff;
+  --text-muted: #a0a0a0;
+  --border-color: #2a3045;
+
+  font-family: 'Inter', system-ui, Avenir, Helvetica, Arial, sans-serif;
+  line-height: 1.6;
   font-weight: 400;
 
-  color-scheme: light dark;
-  color: rgba(255, 255, 255, 0.87);
-  background-color: #242424;
+  color-scheme: dark;
+  color: var(--text-color);
+  background-color: var(--primary-bg);
 
   font-synthesis: none;
   text-rendering: optimizeLegibility;
@@ -13,26 +22,29 @@
   -moz-osx-font-smoothing: grayscale;
 }
 
-a {
-  font-weight: 500;
-  color: #646cff;
-  text-decoration: inherit;
-}
-a:hover {
-  color: #535bf2;
-}
-
 body {
   margin: 0;
   display: flex;
   place-items: center;
   min-width: 320px;
   min-height: 100vh;
+  background-color: var(--primary-bg);
 }
 
-h1 {
-  font-size: 3.2em;
-  line-height: 1.1;
+h1, h2, h3, h4, h5, h6 {
+  color: var(--text-color);
+  margin-top: 0;
+}
+
+a {
+  font-weight: 500;
+  color: var(--accent-color);
+  text-decoration: inherit;
+  transition: color 0.2s;
+}
+
+a:hover {
+  color: #4da3ff;
 }
 
 button {
@@ -42,27 +54,41 @@ button {
   font-size: 1em;
   font-weight: 500;
   font-family: inherit;
-  background-color: #1a1a1a;
+  background-color: var(--accent-color);
+  color: white;
   cursor: pointer;
-  transition: border-color 0.25s;
+  transition: background-color 0.25s, transform 0.1s;
 }
+
 button:hover {
-  border-color: #646cff;
+  background-color: #0b7dda;
 }
+
+button:active {
+  transform: scale(0.98);
+}
+
 button:focus,
 button:focus-visible {
   outline: 4px auto -webkit-focus-ring-color;
 }
 
-@media (prefers-color-scheme: light) {
-  :root {
-    color: #213547;
-    background-color: #ffffff;
-  }
-  a:hover {
-    color: #747bff;
-  }
-  button {
-    background-color: #f9f9f9;
-  }
+input, select {
+  background-color: var(--secondary-alt-bg);
+  border: 1px solid var(--border-color);
+  color: var(--text-color);
+  padding: 0.6em;
+  border-radius: 6px;
+  font-size: 1em;
+  font-family: inherit;
+}
+
+input:focus, select:focus {
+  outline: 2px solid var(--accent-color);
+  border-color: transparent;
+}
+
+ul {
+  list-style: none;
+  padding: 0;
 }