Source Code: (back to article)
<div class="fill-mode-box"></div>

<style>
.fill-mode-box {
width: 100px;
height: 100px;
background-color: purple;
animation: fillMode 3s forwards;
}

@keyframes fillMode {
0% { background-color: purple; }
100% { background-color: orange; }
}
</style>