JSFiddle - React, Tailwind, and code Playground

HTML

<div id="principal">
     
            [Otros contenidos varios...]
     
            <div id="cuadradete"></div>
           
            <div id="cuadradete2"></div>
        </div>

CSS

#principal{
            width: 80%;
            background-color:yellow;
            position:relative;
            margin: 0 auto;
            left: 0;
            right: 0;
            border: 3px solid blue;
            opacity:0.70;
               
            z-index: 0;
        }
     
        #cuadradete{
            width: 100px;
            height: 100px;
            background-color:red;
            position:absolute;
            left:0;
            top:0;
               
            z-index: 1;
        }
     
        #cuadradete2{
            width: 100px;
            height: 100px;
            background-color:blue;
            position:absolute;
            right:0;
            top:0;
               
            z-index: 1;
        }