1、斜邊在左邊三角形

 <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、斜邊在上面的三角形

<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、斜邊在下邊的三角形

 <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、斜邊在右邊的三角形

 <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、等邊三角形（等邊三角形的底邊的高是底邊的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>