- 使用伪元素before和after分别在矩形元素前后加三角形或者直接设置border
- 使用3d旋转矩形，使之看起来像矩形
<html>
<head>
<meta charset="utf-8">
<style>
.trapezoid-0{
border-bottom: 100px solid #fb3;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
height: 0;
100px;
margin: 0 0 20px 0;
}
.trapezoid-1{
border-radius: .5em .5em 0 0;
margin: 20px;
height: 40px;
100px;
background: #fb3;
transform-origin: bottom;
transform: scaleY(1.3) perspective(.5em) rotateX(5deg);
/*scaleY: 纵轴放大1.3倍，使梯形高度等于height；perspective:3d透视效果，元素距离视图的距离*/
}
</style>
</head>
<body>
<div class="trapezoid-0"></div>
<div class="trapezoid-1"></div>
</body>
</html>