1. 对号√实现

<div id='box'></div>

<style>
    #box {
      font-size:16px;
      border-color: #f00;
      border-style:solid;
      width:0.5em;
      height: 1em;
      border-width: 0 0.3em 0.25em 0;
      /**
      旋转实现
      */
      transform:rotate(45deg);
      position:relative;
      left:0.6em;
    }
</style>