These pages are designed to demonstrate a rendering problem that can happen if you are a dunderheaded n00b who doesn't understand MIME types. Basically, the CSS on these pages is dynamic, created by PHP code. If you don't tell the browser it is receiving CSS then it could misinterpret what you send it. In empirical tests, only Firefox and Webkit actually seemed to exhibit this behaviour - other browsers interpret the results as CSS anyway, based on some kind of built-in (non-standard) smarts.
Please tweet me (@dominicsayers) if you want more details.