JSFiddle - React, Tailwind, and code Playground

HTML

<body>
<div id="BG"></div>
<div id="MainWrapper">
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</div>
</body>

CSS

#BG{
   position:fixed;
   left:0;
   right:0;
   top:0;
   bottom:0;
   background:#555 url('http://www.publicdomainpictures.net/pictures/20000/velka/picturesque-sunrise.jpg');
-webkit-filter: grayscale(100%);
-moz-filter: grayscale(100%);
filter: grayscale(100%);
   z-index:-500;
}