三角形：通常会使用透明的border模拟出一个三角形：▲
.traingle {
width:;
height:;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-bottom: 100px solid yellowgreen;
}切角：采用多重线性渐变实现切角
.notching {
width: 40px;
height: 40px;
padding: 40px;
background: linear-gradient(135deg, transparent 15px, yellowgreen 0) top left,
linear-gradient(-135deg, transparent 15px, yellowgreen 0) top right,
linear-gradient(-45deg, transparent 15px, yellowgreen 0) bottom right,
linear-gradient(45deg, transparent 15px, yellowgreen 0) bottom left;
background-size: 50% 50%;
background-repeat: no-repeat;
}梯形：利用伪元素加旋转透视实现梯形
.trapezoid{
position: relative;
width: 60px;
padding: 60px;
}
.trapezoid::before{
content:"";
position: absolute;
top:; right:; bottom:; left:;
transform: perspective(20px) scaleY(1.3) rotateX(5deg);
transform-origin: bottom;
background: yellowgreen;
}当然，还有另一种更简单的方法是利用border实现，借助上面的构造三角形的方法，在矩形两侧构造两个透明的三角形
.trapezoid {
position: relative;
width: 60px;
border-top: 60px solid yellowgreen;
border-left: 40px solid transparent;
border-right: 40px solid transparent;
}五边形：梯形加上三角形，很容易就组合成一个五边形，这里需要借助一个伪元素实现
.pentagon {
position: relative;
width: 60px;
border-bottom: 60px solid yellowgreen;
border-left: 40px solid transparent;
border-right: 40px solid transparent;
}
.pentagon::before {
content:"";
position: absolute;
top: 60px;
left: -40px;
border-top: 60px solid yellowgreen;
border-left: 70px solid transparent;
border-right: 70px solid transparent;
}六边形：看看上面的梯形，如果两个反方向且底边同样大小的梯形，叠加在一起，是不是就能得到一个六边形呢？
.pentagon {
position: relative;
width: 60px;
border-bottom: 60px solid yellowgreen;
border-left: 40px solid transparent;
border-right: 40px solid transparent;
}
.pentagon::before {
content: "";
position: absolute;
width: 60px;
height: 0px;
top: 60px;
left: -40px;
border-top: 60px solid yellowgreen;
border-left: 40px solid transparent;
border-right: 40px solid transparent;
}八边形：六边形都解决了，八边形也不在话下，一个矩形加上两个梯形，可以合成一个八边形
.octagon {
position: relative;
width: 40px;
height: 100px;
background: yellowgreen;
}
.octagon::before {
content: "";
height: 60px;
position: absolute;
top:;
left: 40px;
border-left: 30px solid yellowgreen;
border-top: 20px solid transparent;
border-bottom: 20px solid transparent;
}
.octagon::after {
content: "";
height: 60px;
position: absolute;
top:;
left: -30px;
border-right: 30px solid yellowgreen;
border-top: 20px solid transparent;
border-bottom: 20px solid transparent;
}五角星：3 个三角形叠加旋转在一起实现 ★
.star {
margin: 50px 0;
position: relative;
width:;
border-right: 100px solid transparent;
border-bottom: 70px solid yellowgreen;
border-left: 100px solid transparent;
transform: rotate(35deg) scale(.6);
}
.star:before {
content: ‘‘;
position: absolute;
border-bottom: 80px solid yellowgreen;
border-left: 30px solid transparent;
border-right: 30px solid transparent;
top: -45px;
left: -65px;
transform: rotate(-35deg);
}
.star:after {
content: ‘‘;
position: absolute;
top: 3px;
left: -105px;
border-right: 100px solid transparent;
border-bottom: 70px solid yellowgreen;
border-left: 100px solid transparent;
transform: rotate(-70deg);
}六角星：一个向上的三角形 ▲，叠加上一个向下的三角形 ▼，就可以得到一个六边形
.sixstar {
position: relative;
width:;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-bottom: 100px solid yellowgreen;
}
.sixstar:after {
content: "";
position: absolute;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-top: 100px solid yellowgreen;
top: 30px;
left: -50px;
}八角星：其实使用两个矩形进行旋转拼接就可以了
.eightstar {
position: relative;
width: 100px;
height: 100px;
background-color: yellowgreen;
transform: rotate(30deg);
}
.eightstar::before {
content: "";
position: absolute;
top:;
left:;
width: 100px;
height: 100px;
transform: rotate(45deg);
background-color: yellowgreen;
}十二角星： 最后多角星再来一个十二级角星。在八角星的基础上，再增加一个矩形，就能得到十二角啦。也就是要过第一个伪元素。
.twelvestar {
position: relative;
width: 100px;
height: 100px;
margin-bottom: 100px!important;
background-color: yellowgreen;
transform: rotate(30deg);
}
.twelvestar::before {
content: "";
position: absolute;
top:;
left:;
width: 100px;
height: 100px;
transform: rotate(30deg);
background-color: yellowgreen;
}
.twelvestar::after {
content: "";
position: absolute;
top:;
left:;
width: 100px;
height: 100px;
transform: rotate(60deg);
background-color: yellowgreen;
}椭圆：使用传统的方法画一个椭圆，过去 CSS3 画椭圆，基本上只能借助 border 实现
.ellipse { #这里使用 border 画一个蛋的形状
width: 120px;
height: 160px;
background-color: yellowgreen;
border-radius: 50% 50% 50% 50% / 60% 60% 40% 40%;
}