Fast draw a triangle

1. The downward triangle

width: 0;

height: 0;

border-left: 10px solid transparet;

border-right: 10px solid transparet;

border-top: 10px solid red;

2. improve specific triangle

width: 0;

height: 0;

border-left: 10px solid transparet;

border-right: 10px solid transparet;

border-bottom: 10px solid red;

3. Turn left triangle

width: 0;

height: 0;

border-top: 10px solid transparet;

border-bottom: 10px solid transparet;

border-right: 10px solid red;

4. The right triangle

width: 0;

height: 0;

border-top: 10px solid transparet;

border-bottom: 10px solid transparet;

border-left: 10px solid red;