I avoid using the defaults with the reset code below:
margin:0px; and padding:0px;
For example, what are the default margins for the headin
It varies between browsers. Check each browser's specific default stylesheets to tell.
For Google Chrome for example, it's 0.67em
.
Do know that if you wish to aim for x-browser consistency, you'll have to use a CSS Reset.
The most common one being:
* { padding: 0; margin: 0; }
Although other (and probably better) exist.