Styled alert box without a JS library
<p>I would like to display an alert on my web site.
I could use a library like jQuery, but currently, the site does not use one, and I don't think it is a good idea to add a library just for the sole purpose of an alert box.</p>

<p>Is there any way of styling the alert box, or is there a pure js alternative to something like jQuery modal dialog?</p>
