使用CSS实现椭圆，三角形，五角星等图形

1.椭圆

border-radius 属性是一个简写属性，用于设置四个 border-*-radius 属性。如果省略 bottom-left，则与 top-right 相同。如果省略 bottom-right，则与 top-left 相同。如果省略 top-right，则与 top-left 相同。

border-radius: 2em 1em 4em / 0.5em 3em;

等价于：

border-top-left-radius: 2em 0.5em;
border-top-right-radius: 1em 3em;
border-bottom-right-radius: 4em 0.5em;
border-bottom-left-radius: 1em 3em;

#ellipse {
width: 200px;
height: 100px;
background: red;
color: #fff;
text-align: center;
border-radius: 100px/50px;
/*-webkit-border-radius: 100px/50px;
-moz-border-radius: 100px/50px;*/
}

2.上三角形

#triangle-up {
width: 0;
height: 0;
color: white;
text-align: center;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-bottom: 100px solid red;
}

3.下三角形

#triangle-down {
width: 0;
height: 0;
color: white;
text-align: center;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-top: 100px solid red;
}

4.左三角形

#triangle-left {
width: 0;
height: 0;
color: white;
text-align: center;
border-top: 50px solid transparent;
border-bottom: 50px solid transparent;
border-right: 100px solid red;
}

5.右三角形

#triangle-right {
width: 0;
height: 0;
color: white;
text-align: center;
border-top: 50px solid transparent;
border-bottom: 50px solid transparent;
border-left: 100px solid red;
}

6.左上角是直角的直角三角形

#triangle-topleft {
width: 0;
height: 0;
border-top: 100px solid red;
border-right: 100px solid transparent;
}

7.右上角是直角的直角三角形

#triangle-topright {
width: 0;
height: 0;
border-top: 100px solid red;
border-left: 100px solid transparent;
}

8.左下角是直角的直角三角形

#triangle-bottomleft {
width: 0;
height: 0;
border-bottom: 100px solid red;
border-right: 100px solid transparent;
}

9.右下角是直角的直角三角形

#triangle-bottomright {
width: 0;
height: 0;
border-bottom: 100px solid red;
border-left: 100px solid transparent;
}

10.平行四边形

transform 属性向元素应用 2D 或 3D 转换。该属性允许我们对元素进行旋转、缩放、移动或倾斜。

#parallelogram {
width: 200px;
height: 150px;
margin-left: 30px;
background: red;
-webkit-transform: skew(-30deg);
-moz-transform: skew(-30deg);
-o-transform: skew(-30deg);
-ms-transform: skew(-30deg);
}

11.梯形

#trapezoid {
width: 100px;
height: 0;
border-bottom: 100px solid red;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
}

12.五角星

#star-five {
width: 0;
height: 0;
color: red;
margin: 50px 0;
position: relative;
display: block;
border-left: 100px solid transparent;
border-right: 100px solid transparent;
border-bottom: 70px solid red;
-moz-transfrom:rotate(35deg);
-webkit-transform:rotate(35deg);
-ms-transform:rotate(35deg);
-o-transform:rotate(35deg);
}

#star-five:before {
width: 0;
height: 0;
border-left: 30px solid transparent;
border-right: 30px solid transparent;
border-bottom: 80px solid red;
position: absolute;
top: -45px;
left: -65px;
color: white;
display: block;
content: "";
-moz-transform:rotate(-35deg);
-webkit-transform:rotate(-35deg);
-ms-transform:rotate(-35deg);
-o-transform:rotate(-35deg);
}

#star-five:after {
width: 0;
height: 0;
display: block;
position: absolute;
color: red;
top: 3px;
left: -105px;
border-left: 100px solid transparent;
border-right: 100px solid transparent;
border-bottom: 70px solid red;
content: "";
-moz-transform:rotate(-70deg);
-webkit-transform:rotate(-70deg);
-ms-transform:rotate(-70deg);
-o-transform:rotate(-70deg);
}

13.六角星

#star-six {
width: 0;
height: 0;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-bottom: 100px solid red;
position: relative;
}
#star-six:after {
width: 0;
height: 0;
border-top: 100px solid red;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
position: absolute;
content: "";
top: 30px;
left: -50px;
}

14.正五边形

#pentagon {
width: 54px;
position: relative;
border-width: 50px 18px 0;
border-style: solid;
border-color: red transparent;
}
#pentagon:before {
content: "";
position: absolute;
width: 0;
height: 0;
top: -85px;
left: -18px;
border-width: 0 45px 35px;
border-style: solid;
border-color: transparent transparent red;
}

15.心

#heart {
width: 100px;
height: 90px;
position: relative;
}

#heart:before, #heart:after {
width: 50px;
height: 80px;
left: 50px;
top: 0;
background-color: red;
position: absolute;
content: "";
-moz-border-radius:50px 50px 0 0;
border-radius: 50px 50px 0 0;
-webkit-transform:rotate(-45deg);
-ms-transform:rotate(-45deg);
-moz-transform:rotate(-45deg);
-o-transform:rotate(-45deg);
transform:rotate(-45deg);
-webkit-transform-origin:0 100%;
-ms-transform-origin:0 100%;
-moz-transform-origin:0 100%;
-o-transform-origin:0 100%;
tansform-origin:0 100%;
}

#heart:after {
left: 0;
-webkit-transform:rotate(45deg);
-ms-transform:rotate(45deg);
-moz-transform:rotate(45deg);
-o-transform:rotate(45deg);
transform:rotate(45deg);
-webkit-transform-origin:100% 100%;
-ms-transform-origin:100% 100%;
-moz-transform-origin:100% 100%;
-o-transform-origin:100% 100%;
transform-origin:100% 100%;
}

16.提示对话框、气泡对话框

#talkbubble {
width: 200px;
height: 100px;
background-color: red;
position: relative;
border-radius: 10px;
-webkit-border-radius:10px;
-moz-border-radius:10px;
-ms-border-radius:10px;
-o-border-radius:10px;
}

#talkbubble:before {
width: 0;
height: 0;
right: 100%;
top: 30px;
position: absolute;
content: "";
border-top: 15px solid transparent;
border-right: 30px solid red;
border-bottom: 15px solid transparent;
}

17.钻石

#diamond {
width: 50px;
height: 0;
border-style: solid;
border-color: transparent transparent red transparent;
border-width: 0 25px 25px 25px;
position: relative;
margin: 20px 0 50px 0;
}
#diamond:after {
width: 0;
height: 0;
top: 25px;
left: -25px;
border-style: solid;
border-color: red transparent transparent transparent;
border-width: 70px 50px 0 50px;
position: absolute;
content: "";
}