<div id="random">
</div>

css
#random {
    width: 200px;
    height: 200px;
    border: 1px solid black;
}

script
$('#random').on('mouseover',function() {
    var color = '#'+Math.floor(Math.random()*16777215).toString(16);
    var colorString = '0px 0px 30px 0px ' + color;
    $('#random').css('box-shadow',colorString);
    $('#random').css('-webkit-box-shadow',colorString);
    $('#random').css('-mox-box-shadow',colorString);
});

https://jsfiddle.net/6n0tk3a3/1/
https://stackoverflow.com/questions/31468794/how-to-show-random-color-on-hover-in-css
https://teamtreehouse.com/community/random-background-color