CSS 箭头

1CSS

 .demo4 {
            width: 0px;
            height: 0px;
            border: 10px solid;
            border-color: transparent transparent red transparent;
            /*background-color: lightblue;*/
            margin: 0 auto;
            position: relative;
            /*top: -20px;
            left: 30px;*/
        }

        .demo5 {
            width: 0px;
            height: 0px;
            border: 9px solid;
            border-color: transparent transparent white transparent;
            margin: 0 auto;
            position: relative;
            top: -18px;
            /*left: 30px;*/
        }

　　2：html

<div style="width:20px;height:20px;background-color:lightblue;position:relative;z-index:100">
        <div class="demo4">
        </div>
        <div class="demo5">
        </div>
    </div>