you can change the z-index of a div by using the class .z-{5-120} .
<div class="relative w-12/12 mb-4 bg-blue-600 p-8">
<div class="z-5 bg-green-400 absolute p-4 opacity-50" style="top:0;left:0;">
I'am a div with <b>z-15</b>
</div>
I'am the parent div
</div>