html {
  --s: 200px; /* control the size */
  
  background:
    repeating-conic-gradient(from 30deg,#0000 0 120deg,#3c3c3c 0 180deg) 
     calc(.5*var(--s)) calc(.5*var(--s)*0.577),
    repeating-conic-gradient(from 30deg,#1d1d1d 0 60deg,#4e4f51 0 120deg,#3c3c3c 0 180deg);
  background-size: var(--s) calc(var(--s)*0.577);
  /* 0.577 = tan(30deg)*/
}