Question

How I can replace a JavaScript alert pop up with a fancy alert box?

Answer 1

I think that the window attached to the alert can't be modified since is a system object, and therefore CSS can't do anything there.

So my best bet would be that you would create an HTML element that would mock the alert window, and style it however you want... I, for example, usually go for this: http://jqueryui.com/demos/dialog