Tailwind CSS class .bottom-0 / .bottom-*

<div class="relative h-16 w-16 bg-gray-400 m-2">
  <div class="absolute bottom-0 h-4 w-full bg-teal-400"></div>
</div>
<div class="relative h-16 w-16 bg-gray-400 m-2">
  <div class="absolute bottom-auto top-0 h-4 w-full bg-teal-400"></div>
</div>

.bottom-0 { bottom: 0; }
.bottom-auto { bottom: auto; }