css三角形 - 掘金

<div class="triangle1"></div>
<div class="triangle2"></div>

.triangle1{      
  width: 0;        
  height: 0;        
  border-left: 10px solid transparent;    
  border-right: 10px solid transparent;     
  border-top: 10px solid red;    
}

.triangle2{
  width: 0;
  height: 0;
  border-left: 10px solid transparent;
  border-right: 10px solid transparent;
  border-bottom: 10px solid red;
}