Refactor: centralize theme definitions and enhance dynamic theming capabilities

src/theme.css

@@ -87,6 +87,35 @@
 }
 
 .dot-grid {
+    position: fixed;
+    inset: 0;
+    pointer-events: none;
+}
+
+.dot-grid::before {
+    content: '';
+    position: fixed;
+    inset: 0;
     background-image: radial-gradient(var(--grid-pattern) 1px, transparent 1px);
     background-size: 24px 24px;
+    /* Lock Y so scroll never changes it; keep X drift via CSS variable. */
+    background-position: var(--dot-grid-x, 0px) 0px;
+    will-change: background-position;
+    animation: dot-grid-drift-x 3s linear infinite;
+}
+
+@keyframes dot-grid-drift-x {
+    from {
+        background-position: 0px 0px;
+    }
+
+    to {
+        background-position: 24px 0px;
+    }
+}
+
+@media (prefers-reduced-motion: reduce) {
+    .dot-grid::before {
+        animation: none;
+    }
 }