feat: ux enhancements (animations, dynamic backgrounds, micro-interactions)

src/web/public/style.css

@@ -280,4 +280,106 @@ footer {
     -webkit-background-clip: text;
     background-clip: text;
     -webkit-text-fill-color: transparent;
+}
+
+/* Animations & Micro-Interactions */
+@keyframes fadeIn {
+    from {
+        opacity: 0;
+        transform: translateY(10px);
+    }
+
+    to {
+        opacity: 1;
+        transform: translateY(0);
+    }
+}
+
+@keyframes slideUp {
+    from {
+        opacity: 0;
+        transform: translateY(20px);
+    }
+
+    to {
+        opacity: 1;
+        transform: translateY(0);
+    }
+}
+
+/* Entry Animations */
+.fade-in {
+    animation: fadeIn 0.4s ease-out forwards;
+}
+
+/* Stagger animations for children using nth-child */
+main>* {
+    opacity: 0;
+    /* Initially hidden */
+    animation: slideUp 0.5s ease-out forwards;
+}
+
+main>*:nth-child(1) {
+    animation-delay: 0.1s;
+}
+
+main>*:nth-child(2) {
+    animation-delay: 0.2s;
+}
+
+main>*:nth-child(3) {
+    animation-delay: 0.3s;
+}
+
+main>*:nth-child(4) {
+    animation-delay: 0.4s;
+}
+
+/* Dynamic Background */
+body::before {
+    content: '';
+    position: fixed;
+    top: 0;
+    left: 0;
+    width: 100vw;
+    height: 100vh;
+    background:
+        radial-gradient(circle at 15% 50%, hsla(var(--primary-h), var(--primary-s), var(--primary-l), 0.08), transparent 25%),
+        radial-gradient(circle at 85% 30%, hsla(var(--secondary-h), var(--secondary-s), var(--secondary-l), 0.08), transparent 25%);
+    z-index: -1;
+    pointer-events: none;
+}
+
+/* Link Interactions */
+a {
+    position: relative;
+    transition: color 0.2s ease, opacity 0.2s ease;
+}
+
+header nav a::after {
+    content: '';
+    position: absolute;
+    bottom: -4px;
+    left: 0;
+    width: 0%;
+    height: 2px;
+    background: var(--primary);
+    transition: width 0.3s cubic-bezier(0.4, 0, 0.2, 1);
+}
+
+header nav a:hover::after {
+    width: 100%;
+}
+
+/* Accessibility: Reduced Motion */
+@media (prefers-reduced-motion: reduce) {
+
+    *,
+    *::before,
+    *::after {
+        animation-duration: 0.01ms !important;
+        animation-iteration-count: 1 !important;
+        transition-duration: 0.01ms !important;
+        scroll-behavior: auto !important;
+    }
 }