How to make multiple page share the same header/footer so I don't need to update every page when I want to modify the header/footer. I don't want to use freameset tag as there will be an ugly bar between different frames. So how can I make this shared header/footer using pure HTML? I'm not using any framework.
Short answer: you can't. Not using pure HTML. The best way to do it is to put the header and footer in their own files, then load them in using PHP or javascript.