Problem with the Categories-Tabs Menu

[Tjekija]

Have been searching for hours now, to find information to solve my problem:
When I´m setting the Categories-Tabs Menu to ON, in my layout-settings, to have my Categories also showing across the header, it just continues in a long line instead of being put into two or more lines in the header.
The header itself is also a bit shorter than the rest of the layout in my shop and in an ugly grey color on top of it!
(Please see my screenshot).
How do I get the catergories to not continue out of the layout/template?
And how do I get the category header to get same lenght as my main logo and log in/log out header? And I also want to change the gray color to another.
Thanks in advance.

[stevesh]

Find this in your sylesheet and remove the red part:

#navMain ul li a, #navSupp ul li a, #navCatTabs ul li a {
text-decoration: none;
padding: 0em 0.5em;
margin: 0;
color: #ffffff;
white-space: nowrap;
}

For the other questions, we'll need a link to the site.