I created a website template using HTML and CSS so that the design lays flush against the top of the page.

I have since inserted lots of PHP into it (and used some 'includes') and now an unwanted margin has appeared above the body of the web page. This could be easily fixed using a bit of CSS to absorb the margin, i.e.

body {
margin-top: -20px;

However, the size of the margin differs depending on the browser you are using:-
Google Chrome, Safari: 20px margin
Firefix, Opera: 26px margin
Internet Explorer: Everything is completely messed up using IE!

I can't figure out what is causing this margin to appear, or how to remedy the problem with a single fix for both sets of browsers (I'm not going to worry about IE for the time being given the whole design has been inexplicably skewed).

Any help gratefully received,