1.css
.parent{
position:relative;
width:100px;
height:100px;
}
.parent span {
display:block;
width:0;
height:0;
border-width:10px;
border-style:solid;
border-color:transparent transparent #f00 transparent; //方向可自行调整
position:absolute;
top:-20px;
left:20px;
}
2. html
<div class="parent"><span></span></div>
3.效果
4.兼容性
主要是对transparent兼容性问题
