Newbie needs help with CSS

Hi there. I am very new to web design but like the look of Zen Cart for my store. I have been following a tutorial in an old magazine to help me through the set up and for the most pasrt I have had success.
I am now trying to change the colour of the site using the CSS. The tutorial says:
Go to TABLE.headerNavigation, select the background-color and change the hex colour code. Save the CSS file and upload it back to the appropriate folder.'
I have tried this repeatedly but nothing seems to change, I just keep getting the default brown Zen Cart colour scheme.
I am at a loss so if anybody could help me out here I would be very grateful.

Magazinerack, I think you will find that the default brown is a jpg graphic in front of the colour, you will have to remove it from the CSS to be able to see the colour changes that you make. Either delete it, replace it or hide it by adding the bold below to your code.

/*background-image: url(../images/tile_back.jpg);*/

Brilliant. Thanks for your help, that has done what I was looking for.