💫 (button) add animation

src/styles/app.scss

@@ -49,3 +49,14 @@ button {
 a {
   color: white;
 }
+
+// transition
+
+.fade-enter-active,
+.fade-leave-active {
+  transition: opacity 0.3s ease;
+}
+.fade-enter,
+.fade-leave-to {
+  opacity: 0;
+}