css3实现三角形

div{
    border: 1px solid #dddddd;
    padding: 4px 40px 4px 8px;
    position: relative;
}
div:after{
    content: ' ';
    margin-top: -5px;
    display: block;
    position: absolute;
    right: 8px;
    top: 50%;
    width: 0;
    height: 0;
    border-left: 12px transparent solid;
    border-right: 12px transparent solid;
    border-top: 12px #000000 solid;
}