<div id="square1">

  </div>



#square1{
width: 0; height: 0; border: 10px solid;
 border-color: green transparent red transparent; 
border-width: 0px 10px 10px 10px;}

沙漏的话
border-width: 0px 10px 10px 10px;
就是 border-width: 10px 10px 10px 10px;