CSS/Javascript code to provide image border for many sizes of HTML div

CSS/Javascript code to provide image border for many sizes of HTML div

I'm intending to write a HTML5/Javascript game to run in modern browsers.
It will need dialog boxes (i.e. modal popups) whose borders would be made
of images (e.g. one for the vertical, one for the horizontal, one for each
corner). The popups, and therefore border, should contain and size to a
div (containing text or whatever). There will be lots of different size
popups.
I hope that my requirements are clear enough. Can I do this with just CSS?
Are there some sample CSS 'libraries' to do this? Or do I need to use
Javascript (or a combination of CSS and Javascript) and, again, if so
there any example or libraries I can use?