<div class="foo">This is some content!</div>

.foo {
  box-sizing: border-box;
  position: relative;
  width: 300px;
  height: 300px;
  padding: 15px;

  &::before {
    background: #fff;
    bottom: 15px;
    box-shadow: 0px 2px 8px 2px #333;
    content: "";
    display: block;
    left: 15px;
    position: absolute;
    right: 15px;
    top: 15px;
    z-index: -1;
  }
}