comment request for new website

Hello,

Please comment on this website I'm building from scratch:
http://www.eerstehulpbijinternet.nl/test/test_pile.html

Specifically:
1. I want to use the background image, CENTERED automatically within
the browser, however I also want to be able to freely position
textblocks on top of that image, which should be positioned RELATIVE
TO THAT IMAGE. To me it looks now that as soon as a choose relative
positioning that it is impossible to work with layers?

2. I have three layers now that do indeed appear in the correct order;
then I added a fourth, but that appears behind all other layers now.
Why is that?

If possible I would like to use only html and css.