JSFiddle - React, Tailwind, and code Playground

HTML

<div class='container'>
    <div class='opacity'></div>
    <div class='text'>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla mauris est, dictum vitae sagittis ut, rutrum in nisi. Quisque congue risus et felis rutrum quis interdum massa condimentum. Nullam cursus porta leo, sit amet porttitor dui dignissim eget. Vivamus auctor venenatis eros ullamcorper accumsan. In hac habitasse platea dictumst. Donec.</div>
</div>

CSS

body { background:url("http://i.imgur.com/NUBzS.jpg"); font:normal normal 12px tahoma; }

.container { 
    padding:20px; 
    border:1px solid black;
    position:relative;
    margin:20px;
}
.opacity {
    position:absolute;
    width:100%;
    height:100%;
    background:black;
    opacity:0.3;
    left:0;
    top:0;
}
.text { position:relative; color:white; }