The first thing you need to know is that the whole web site on a Cobox device can't be more than 64KB in size. That's not much room, but you can fit a few web pages and an applet or two, if you're careful.
The HTML files for the Cobox devices is plain HTML, no frills. It's all interpreted by the client browser, there's no way to access any of the device's properties using HTML alone. So you can put whatever HTML, images, and other static files that you want to on the Cobox, as long as it fits in the 64KB memory.