JSFiddle - React, Tailwind, and code Playground

HTML

<div class="block"></div>

SCSS

.block{
  width: 100px;
  height: 100px;
  position: relative;
  border: 1px solid green;
  background: #fff;
  border-radius: 3px;
  margin: auto;
  &:after {
    content: '';
    position: absolute;
    z-index: -1;
    bottom: 0;
    width: 100%;
    height: 2px;
    box-shadow: 0 0 4px rgba(0, 0, 0, 1);
  }
}