fix: rainbow and put it in core.css for everyone!

core.css

@@ -59,3 +59,31 @@ button:active {
 button {
   transition: transform 0.1s cubic-bezier(0.4, 0, 0.2, 1);
 }
+
+.rainbow {
+  text-decoration: underline;
+  background: linear-gradient(
+    to right,
+    #6666ff,
+    #0099ff,
+    #00ff00,
+    #ff3399,
+    #6666ff
+  );
+  -webkit-background-clip: text;
+  background-clip: text;
+  color: transparent;
+  animation: rainbow-animation 5s ease-in-out infinite;
+  background-size: 400% 100%;
+}
+
+@keyframes rainbow-animation {
+  0%,
+  100% {
+    background-position: 0 0;
+  }
+
+  50% {
+    background-position: 100% 0;
+  }
+}