<div class="test"></div>
.test {
  position: relative;
  margin: 20px;
  background: #000;
  min-height: 100px;
}

.test:before {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  height: 10px;
  background-color: #000;
  background-image: linear-gradient( 135deg, rgba(255, 255, 255, 1) 34%, rgba(255, 255, 252, 0) 0%), linear-gradient( -135deg, rgba(255, 255, 255, 1) 50%, rgba(255, 255, 255, 0) 50%);
  background-size: 18px 10px;
  background-repeat: repeat-x;
}
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