HTML：spa
<div class="top_01"><i></i></div>
<div class="top_02"><i></i></div>
<div class="top_03"><i></i></div>class
CSS:
.top_01 i{display:block;height:0px;width:0px;border:10px solid;border-color:yellow transparent transparent transparent;}
.top_02 i{display:block;height:0px;width:0px;border:20px solid;border-bottom:none; border-color:yellow transparent transparent}
.top_03 i{display:block;height:0px;width:0px;border-width:40px 40px 0;border-style:solid;border-color:yellow transparent transparent}top