HTML代码：
<div class="test1"></div>
<div class="test2"></div>
<div class="test3"></div>
<div class="test4"></div>
CSS代码：
.test1{
width: 0;
height: 0;
border-right: 50px solid transparent;
border-bottom: 50px solid blue;
border-left: 50px solid transparent;
}
.test2{
width: 0;
height: 0;
border-top: 50px solid transparent;
border-bottom: 50px solid transparent;
border-left: 50px solid orange;
}
.test3{
width: 0;
height: 0;
border-top: 50px solid black;
border-right: 50px solid transparent;
border-left: 50px solid transparent;
}
.test4{
width: 0;
height: 0;
border-top: 50px solid transparent;
border-right: 50px solid red;
border-bottom: 50px solid transparent;
}
由此可见 ，控制css的border即可实现4种角度的三角形
