第一对渐变颜色为yellow, 第二对渐变颜色为black

div{ 
   border-radius: 20px;
   width: 70%;
   height: 400px;
   margin:  50 auto;
   background: repeating-linear-gradient(
     45deg,
     yellow 0px,
     yellow 40px,
     black 40px,
     black 80px
   );
   
 }