<button on:click> Click me </button> <style> button { height: 4rem; width: 8rem; background-color: #aaa; border-color: #f1c40f; color: #f1c40f; font-size: 1.25rem; background-image: linear-gradient(45deg, #f1c40f 50%, transparent 50%); background-position: 100%; background-size: 400%; transition: background 300ms ease-in-out; } button:hover { background-position: 0; color: #aaa; } </style>