JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="content">
        <h1>Hello, World</h1>
    </div>
</div>

CSS

.container {
    background-color: red;
    width: 500px;
    height: 500px;
    position: relative;
}
.content {
    background-color: blue;
    width: 250px;
    position: relative;
    z-index: 1;
}
.container::before {
    content:"";
    display: block;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    z-index: 1;
    background-color: rgba(255, 255, 255, .8);
}