Unable to find background width MainMenu Corporate Clean theme

The main menu of the Corporate Clean theme is a dropdown menu.
This makes it somewhat hard to see the right CSS code in FireBug. Therefor I've changed about all the #header-menu codes one by one without any succes.

A image to illustrate the problem.
When on the main menu in this case the text -L'Ortie assocation- the menu rolls out.
You can see horizontal black lines (A+red arrows added to image) that seperate the different sub menu items. This is the width I want the menu to be. 'Funny' enough the hover (not to been seen on image) shows the right width.
I want the black blackground (B+red arrows added to image) of the menu items to been of the same width as the black lines.
I gave all this CSS code -width: 150px;- as are the lines... nothing changed.
The CSS for the main menu:

/* 
* Main-menu 
*/
/* 1st Level */
#header-menu ul.menu  { display:block; padding:0; margin:0; position:relative; z-index:100;}


#header-menu ul.menu li { display:inline-block; float:left; vertical-align: middle; padding:0; margin:0; border-width: 1px; }

#header-menu ul.menu li a { outline:none; text-decoration: none; margin:0 35px 0 0; color:#ffffff; font-size:18px; font-weight:normal; text-align:center; text-transform:undercase; 
font-family: Myriad Pro,"Lucida Grande","Lucida Sans Unicode",Segoe UI,Helvetica,Arial,sans-serif; display:block;
}

#header-menu ul.menu li a:hover, #header-menu ul.menu li a.active { color: #e844f9;
}

#header-menu ul.menu li a:after { content: none; }

#header-menu ul.menu li.expanded { position: relative; }

#header-menu ul.menu li.expanded a { background:transparent url('images/main-menu-expanded.png') no-repeat center right; padding:0 15px 0 0; }

/* 2nd Level */

#header-menu ul.menu li.expanded ul.menu { width: 150px; z-index:100; padding:0; background: #222222; display: none; position: absolute;}

#header-menu ul.menu li.expanded:hover, #header-menu ul.menu li.expanded:hover > ul.menu { display:block;}

#header-menu ul.menu li.expanded ul.menu li a { padding:10px; margin:0; display:block; width:150px; text-align:left; line-height:130%; background:none; font-size:12px; border-bottom:1px solid #353535;}

#header-menu ul.menu li.expanded ul.menu li.expanded { background:transparent url('images/main-menu-arrow.png') no-repeat center right; width: 150px;}

#header-menu ul.menu li ul.menu li a:hover {  background:#1b1b1b; color: #f13ed4; width: 150px;}

#header-menu ul.menu li.expanded ul.menu li.expanded a:hover { background:#1b1b1b url('images/main-menu-arrow.png') no-repeat center right; width: 150px;
}

#header-menu ul.menu li.expanded ul.menu li.leaf a:hover { background:#1b1b1b;  width: 150px;

}

/* 3rd, 4th, 5th, (...) level  */
#header-menu ul.menu li.expanded ul ul { display: none; left: 120px; top:0; padding:0; width: 150px}

Drives me..