SOURCE

<div class="coupon-card"></div>


<div class="diamond"></div>

.coupon-card {
    width: 200px;
    height: 120px;
    background-image: radial-gradient(circle at 100px -8px , transparent 20px, #b4a078 21px);
  }

  .diamond{
    width: 55px;
   height: 55px;
    border: 29px solid transparent;
    box-sizing: content-box;
    position: relative

  }
  .diamond::before{
    content: "";
    position: absolute;
    top: 0; left: 0; bottom: 0; right: 0;
    z-index: -1;
    background: #b4a078;
    transform: rotate(45deg);
  }