Q:

CSS, HTML - Site displays very wrong in Internet Explorer

Please look at this link - http://sklepylaserowe.test.dih.pl/.
It displays well in Firefox, Chrome and Opera - but it's messed up in Internet Explorer (8 and 9). What could be a reason of it? (From list "Wybierz województwo", please select "śląskie", click "Dalej >>", and click on link that appears, to hide that overlay window)
Many basic CSS commands don't work, like:
margin:0 auto;

A:

You are failing to start the document with a Doctype, this triggers Quirks mode in which browsers emulate the bugs of their ancient ancestors.
Not supporting auto margins for centring is one of these bugs in IE (it was fixed in IE 6). 
Validate your HTML. You cannot put any tags before the Doctype.

