JSFiddle - React, Tailwind, and code Playground

HTML

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JavaScript

var images = [ 'http://tinyurl.com/qhhyb8k'
             , 'http://tinyurl.com/nqw2t9b'
             , 'http://tinyurl.com/nkogvoq'
       //    , 'url 4'
             ]
,    image = images[ (Math.random() * images.length)|0 ]
; //end vars

window.onload=function(){
    document.body.style.background=
        "url('"+image+"') no-repeat center center fixed";
    document.body.style.backgroundSize=
        "cover";  // width% height% | cover | contain 
};