<div class="promo">
  <div class="back"></div>
</div>

  .back{
    background: repeating-linear-gradient(-45deg, #8852cd, #8852cd 1px, transparent 1px, transparent 3px);
    background-color: #854ecc;
    border-radius: 50% 50% 8px 8px / 8px 8px;
    width: 99%;
    height: 20px;
    position: absolute;
    top: -6px;
    left: 50%;
    transform: translateX(-50%);
  }
  
 .promo { position: relative;
width: 500px;
height: 100px;
  padding-top:25px;
  box-sizing: border-box;
  display: inline-block;
  background: repeating-linear-gradient(-45deg, #8852cd, #8852cd 1px, transparent 1px, transparent 3px);
  background-color: #854ecc;
  border-radius:8px;
  color: #fff;
  box-shadow: 1px 2px 79px rgba(0, 0, 0, .26);