JSFiddle - React, Tailwind, and code Playground

HTML

<div class="caret"></div>
<p>
 将宽高都设置为0<br/>
 border-color:red green yellow blue;将变宽四个方向颜色设置成不同的颜色以便观察
</p>

CSS

.caret{
  height:0;/*将宽高都设置为0*/
  width:0;
  border:100px solid #000;
  border-color:red green yellow blue;
}
p{color:red;}