버튼 배경 css

<div id="buttons1">
  <button>
    button
    <span class="bg"><span>button</span></span>
  </button>
</div>

#buttons1 button { overflow: hidden;position: relative; width: 200px;border-radius: 20px;}
#buttons1 button .bg {overflow: hidden;position: absolute;top: 0;left: 0;
    width: 0;
    height: 100%; transition: 0.3s;}
#buttons1 button:hover .bg{ width: 100%;}
#buttons1 button span span {display: block;
    width: 200px;
    height: 80px;background-color: #ae5e9b;line-height: 80px;color: #fff;}