Fullscreen Theme: set fixed width for menu and sub-menu

Hello,

I’m building a website using the free version of the Fullscreen Theme by Graph Paper Press.

The menu is a Superfish menu, I found a copy online (CSS here).

I want to fix the width of the menu and sub-menus so they align neatly.

I managed to fix the width of the menu to 100px (see below), but I cannot figure out how to fix the width of the sub-pages.

#branding { background: #fff; color:#000; position:absolute; z-index: 4; left: 0px; top:240px; height:40px; padding:40px; zoom:1; width: 100%; margin:auto; clear: both; display: block; }
#branding a, #masthead a { background: #fff; color:#000; text-decoration:none; font-size:16px; width: 100px }
#branding h1 a, #masthead h1 a { color:#000; }
#branding h1, #masthead h1 { text-transform:uppercase; font-weight:bold; margin:0 ;}
#branding a:hover { background: #5dbbbd; color:#fff; }
#branding .description { text-align:left;}
.brand-wrap { float:left; }

Any help would be greatly appreciated!