与白色边界的三角形

Question

如何使用CSS创建带白色边框的三角形？如下图所示。

当我添加此css

时

.triangle {
    width:0;
    height:0;
    border-top: 20px solid transparent; 
    border-left: 20px solid white; 
    border-bottom: 20px solid transparent;
    position:relative;

}
.triangle:before {
    content:'';
    width:0;
    height:0;
    border-top: 10px solid transparent; 
    border-left: 10px solid red; 
    border-bottom: 10px solid transparent;
    position:absolute;
    top:-10px;
    left:-17px;
}

结果是

Answer 1

CSS：

.triangle {
    width:0;
    height:0;
    border-top: 20px solid transparent; 
    border-left: 20px solid white; 
    border-bottom: 20px solid transparent;
    position:relative;

}
.triangle:before {
    content:'';
    width:0;
    height:0;
    border-top: 10px solid transparent; 
    border-left: 10px solid red; 
    border-bottom: 10px solid transparent;
    position:absolute;
    top:-10px;
    left:-17px;
}

HTML：

<div class="triangle"></div>

Fiddle