.hvac-zigzag {
  position: relative;
  overflow: visible;
}

.hvac-zigzag::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: -12px;
  width: 100%;
  height: 12px;
  background-repeat: repeat-x;
  background-size: auto 12px;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='40' height='12'%3E%3Cpolygon points='0,0 20,12 40,0' fill='%23A50000'/%3E%3C/svg%3E");
}