JSFiddle - React, Tailwind, and code Playground

HTML

<div id="semi-transparent">
<div id="full-opaque">HELLO!</div>
</div>

CSS

#semi-transparent {
 background: rgba(0,0,0,0.8);   
    width: 300px;
    height: 600px;
}
#full-opaque {
 background: #ffffff;
    width: 100px;
    height: 50px;
}
body {
 background: url(http://www.3quarks.com/images/backgrounds/Texture0402.gif);   
}