JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    
</body>

JavaScript

var fondos = ["http://www.w3.org/html/logo/downloads/HTML5_Logo_512.png","http://www.muylinux.com/wp-content/uploads/2012/12/html5.jpg","http://www.mobile.safilsunny.com/wp-content/uploads/2013/01/html5.png","http://www.carlosblanco.eu/blog/wp-content/uploads/2012/08/CSS3Logo_406A9E5E.jpg","http://www.w3.org/html/logo/img/class-header-css3.jpg","http://www.onbile.com/info/wp-content/uploads/2012/07/html5-css3.jpg","http://www.tutosytips.com/wp-content/uploads/2012/08/responsive-design-css3.jpg"];

var fecha = new Date();
var dia = fecha.getDay();

document.body.style.backgroundImage = "url(" + fondos[dia] + ")";