I am developing a Wordpress theme on your own, and to date everything's running smoothly (it's my very first time). However, beneath the admin bar I've 18 pixels of whitespace that wasn't during my static HTML page before Wordpress-ing up. See below for any screenshot:

enter image description here

Nowhere part may be the header, that ought to be flush using the admin bar. Can there be any apparent reason behind this happening?

you may could provide us with more css. That may have 1000's of reasons. If you do not use firebug or any other developer tools you need to defenitley make sure that out. With this particular tools you are able to click in the place using the css element you need to see and find out the characteristics...

https://addons.mozilla.org/de/firefox/addon/firebug/

or click at chrome around the preferences from the browser...than "tools" after which "developer tools"

If you do not discover the answer with this particular tools, publish us some css out of your stylesheet

We are short on information here. We have to call at your CSS to have an accurate answer.

In either case, should you log out, may be the margin there? I am confident it's. I really think you are getting a margin-top or padding-top in your container/header/whatever element is on the top.

If there's no margin, your CSS is most likely disturbing the admin bar. You most likely set a margin-bottom with an element that suits either your class, tag or structure from the admin bar.

Should you still aren't seeing anything, there's a really slim chance that could be browser-related. When the other solutions did not work, try adding a CSS reset.