How to reduce height of bar above header background image?

Using v1.3.7 and 'classic' template

How do I reduce the height of the top full width bar (displaying - Home : Login) above the header background image?

I have made a smaller background tile of 24px height but can't see the place in any CSS that specifies the bar height. The nearest I could find was #navMainWrapper which has a height set at 1% (of what???), changing that to 24px made no difference.

First, I hope you've created your own template and aren't modifying the files in the /classic/ folders. If you modify the files in the /classic/ or /template_default/ folders, all of your changes will be overwritten (LOST) during an upgrade/update.

To answer your question, to change that line look in your stylesheet for:

#navMain ul, #navSupp ul, #navCatTabs ul {
	margin: 0;
	padding: 0.5em 0em;
	list-style-type: none;
	text-align: center;
	line-height: 1.5em;
		}

You can adjust the line-height accordingly. You may need to adjust the font size elsewhere, but probably only if you're planning on making that line very small.