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

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

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