.box-shadow::after {
  content: "";
  position: absolute;
  width: 100%;
  bottom: -1px;
  z-index: -1;
  box-shadow: 0 0 4px 1px rgba(0, 0, 0, 0.4);
}

.element {
  position: relative;
}

<div class="element box-shadow">
  <!-- content here -->
 </div>