console 命令行工具 X clear

console

<div class="box">
  <div class="inner_box">子元素宽度：500px * 50% = 250px</div>
</div>

.box {
  width: 500px;
  padding: 100px;
  height: 100px;
  border: 1px solid red;
}

.inner_box {
  width: 50%;
  height: 50px;
  border: 1px solid gray;
}