div{
       width: 100px;
       height: 100px;
       border: 100px solid black;
   border-left-color:darkcyan;
   border-right-color: rgb(255, 0, 157);
   border-top-color:royalblue;
   border-bottom-color: blueviolet;    
   }

 div{
       width: 0;
       height: 0;
       border: 100px solid black
 
;
   border-left-color:coral;
   border-right-color:transparent;
   border-top-color:transparent;
   border-bottom-color:coral;    
   }

Transparent

用css畫的一個圖形 空心正方形+四邊四色