console 命令行工具 X clear

console

<body>
<div class="ad"></div>
<div class="a"></div>
<div class="a"></div>
<div class="a"></div>
  
</body>

.a:first-of-type {
  background: red;
}

div {
  width: 100%;
  height: 100px;
  background: #aaa;
  border: 10px solid #444;
  box-sizing: border-box;
}