JSFiddle - React, Tailwind, and code Playground

HTML

<div class="rectangle-box">
  <div class="rectangle-red"></div>
</div>

CSS

.rectangle-box {
	    width: 200px;
	    height: 30px;
	    background: #808080;
	    opacity: 0.3;
	    float: right;
    }

    .rectangle-red {
	    width: 65px;
	    height: 30px;
	    background: #ff4742;
	    opacity: 1;
	    float: left;
    }