☀【布局】三角

Creating Triangles in CSS
http://jonrohan.me/guide/css/creating-triangles-in-css/
<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="utf-8">
    <title></title>
    <style>
        .wrap {
            width: 100px;
            background: #F00;
        }
        .box {
            margin-bottom: 10px;
            margin-right: auto;
            margin-left: auto;
        }
        .box-1 {
            border-width: 6px;
            border-style: solid;
            border-color: #FF0;
        }
        .box-2 {
            border-width: 6px;
            border-style: solid dashed;
            border-color: #FF0 transparent;
        }
        .box-3 {
            border-width: 6px 6px 0;
            border-style: solid dashed;
            border-color: #FF0 transparent;
        }
        .box-4 {
            width: 0;
            height: 0;
            overflow: hidden;
            border-width: 6px 6px 0;
            border-style: solid dashed;
            border-color: #FF0 transparent;
        }
    </style>
</head>
<body>
    <div class="wrap">
        <div class="box box-1"></div>
        <div class="box box-2"></div>
        <div class="box box-3"></div>
        <div class="box box-4"></div>
    </div>
</body>
</html>