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

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

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