You need to make a decision as to how you want the page to change when you zoom in/out. Do you expect elements to scale with the page or have the page close around them.
The former must be handled by using scaleable CSS3 sizing types, like % (although now there are more) Scroll down to RELATIVE LENGTHS
]. This can be difficult.
The later is somewhat easily handle by using position:absolute style and locating the items where you want on the page. Scaling the page (zoom in) will have you see less and less of the page content but it will stay where it is supposed to be.
Make good use of that link: it has HTML and CSS tutorials that will be quite helpful, including example that are live and allow you to test modifications.