CSS還是比較強大的，可以實現中國古典的“陰陽八卦圖”等形狀。

正方形

  #rectangle {
      width: 200px;
      height: 100px;
      backgrount-color: red;
  }  #circle {
      width: 100px;
      height: 100px;
      -webkit-border-radius: 100px;
         -moz-border-radius: 100px;
              border-radius: 100px;
      background-color: red;
  }
 

橢圓

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

直角三角形

直角邊left-top

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

直角邊right-top

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

梯形

  #parallelogram {
       width: 150px;
       height: 100px;
       -webkit-transform: skew(20deg);
          -moz-transform
 
: skew(20deg);
               transform: skew(20deg);
       background: red;
  }

雞蛋

  #yin-yang {
       width: 96px;
       height: 48px;
       background: #eee;
       border-color: red;
       border-style: solid;
       border-width: 2px 2px 55px 2px;
       border-radius: 100%;
       position: relative;
  }

  #yin-yang:before {
       content: "";
       position: absolute;
       top: 50%;
       left: 0;
       background: #eee;
       border: 18px solid red;
       border-radius: 100%;
       width: 12px;
       height: 12px;
  }

  #yin-yang:after {
       content: "";
       position: absolute;
       top: 50%;
       left: 50%;
       background: red;
       border: 18px solid #eee;
       border-radius:100%;
       width: 12px;
       height: 12px;
  }