console 命令行工具 X clear

console

// document.getElementById('button').focus()

<script src="//unpkg.com/vue/dist/vue.js"></script>
<script src="//unpkg.com/element-ui@1.4.5/lib/index.js"></script>
<div id="app">
  <button id="button">focus</button>

</div>

@import url("//unpkg.com/element-ui@1.4.5/lib/theme-default/index.css");
button {
  background: red
}
button:focus {
  background: green;
}