css 画三角形

1、斜边在左边三角形

 <style>
        .triangle {
            border-top: 50px solid transparent;
            border-bottom: 50px solid transparent;
            border-left: 50px solid #000;
            width:0;
            height:0;
        }
 </style>
 <div class="triangle"></div>

2、斜边在上面的三角形

<style>
        .triangle {
            border-left: 50px solid transparent;
            border-right: 50px solid transparent;
            border-top: 50px solid #000;
            width:0;
            height:0;
        }
 </style>
 <div class="triangle"></div>

3、斜边在下边的三角形

 <style>
        .triangle {
            border-left: 50px solid transparent;
            border-right: 50px solid transparent;
            border-bottom: 50px solid #000;
            width:0;
            height:0;
        }
 </style>
 <div class="triangle"></div>

4、斜边在右边的三角形

 <style>
        .triangle {
            border-top: 50px solid transparent;
            border-bottom: 50px solid transparent;
            border-right: 50px solid #000;
            width:0;
            height:0;
        }
 </style>
 <div class="triangle"></div>

5、等边三角形（等边三角形的底边的高是底边的1/sqrt(2)倍）

 <style>
        .triangle {
            border-left: 40px solid transparent;
            border-right: 40px solid transparent;
            border-bottom: 28px solid #000;
            width:0;
            height:0;
        }
 </style>
 <div class="triangle"></div>