<div class="box">
  <div class="fill-available">
    階層式樣式表是一種用來為結構化文件添加樣式的電腦語言，由W3C定義和維護。
  </div>
</div>
.box{
  height: 200px;
}
.fill-available {
    display: inline-block;
    width: -webkit-fill-available;
    width: -moz-fill-available;
    width: -moz-available;
    width: fill-available;
    background-color: pink;
}

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