You are correct, you should be editing the "navigation.css" file. Look for 6 different times 165px are called.

You will edit any width : 165px and left: 165px. Make sure they all match you new width.

You also might need to add more width of the navigation container here:
/css/standard.css
under: "/* MENU AND NAVIGATION POSITIONING AND WIDTH */"

Thanks Mike, it´s done!
Cheers!!!

Mike,
Is it possible to make only the sub-menu items wider, while keeping the main menu as you have designed it?

You can with customizations. You can learn about our drop-down menu solution here:
http://users.tpg.com.au/j_birch/plugins/superfish/

We are using the "supersubs" solution so the sub-menus resize to the text size.

Why are my sub-menus not resizing to the text?

http://www.staplesandcharles.com/ (Recent Projects)

Ahh you are correct you can adjust the sub-menu width here (we aren't using supersubs in Broadside):

/css/navigation.css

The width is set in multiple places as 165px.

After some trial and error I seem to have figured it out. I had to add the lines

.sf-vertical li li {
width: (width)px !important;
}

and then change the shadows to be the matching width.

Thank you.

While on the topic...
How/where would I format or change the label "MENU" of the navigation menu?
I would like for it to match the typeface and size of pop-up labels.

Glad you got the sub-menus sorted.

You can adjust the MENU label in the css here:
/css/standard.css

section "/* MENU AND NAVIGATION POSITIONING AND WIDTH */"

.navigation-menu h1