;)

gistfile1.js

(function () {
    var
        g = 'radial-gradient(farthest-corner at %spx %spx , transparent 0%, #f00 100%)',
        t = 30000,
        b = $(document.body),
        d = $('<div></div>'),
        f = function () {
            var ww = $(window).width(), wh = $(window).height(),
                x = g.replace('%s', ww / 2).replace('%s', wh / 2);
            d.css('background', x).css('background','-webkit-' + x);
            d.css('width', ww).css('height', wh).fadeIn(2000, function () {

                d.fadeOut(2000, function () {
                    d.css('width', 0).css('height', 0);
                    setTimeout(f, Math.random() * t);
                });
            });
        };

    $.getScript('https://raw.githubusercontent.com/jquery/jquery-color/master/jquery.color.js');

    d
        .css('zIndex', 111)
        .css('display', 'none')
        .css('position', 'fixed')
        .css('top', 0);

    b.append(d);

    setTimeout(f, t);
}());