SOURCE

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

.coupon{
  width: 300px;
  height: 100px;
  position: relative;
  background: radial-gradient(circle at right bottom, transparent 10px, #ffffff 0) top right /50% 51px no-repeat,
    radial-gradient(circle at left bottom, transparent 10px, #ffffff 0) top left / 50% 51px no-repeat,
    radial-gradient(circle at right top, transparent 10px, #ffffff 0) bottom right / 50% 51px no-repeat,
    radial-gradient(circle at left top, transparent 10px, #ffffff 0) bottom left / 50% 51px no-repeat;
  filter: drop-shadow(2px 2px 2px rgba(0,0,0,.2));
}