<div></div>

div {
  height: 400px;
  width: 400px;
  margin: 0 auto;
}

div {
  background-image: conic-gradient(
      transparent 0.25turn,
      #000 0.25turn 0.5turn,
      transparent 0.5turn 0.75turn,
      #000 0.75turn
    ),
    linear-gradient(to bottom, blue, blue);
  background-size: 20% 20%;
  border: 1px solid;
  background-repeat: repeat;
}