Full page width main menu

Wordpress 3.8.1
Enfold 2.4.5
http://longislandteacher.com/cmxprocess_v2

Great theme, thanks.
Would like to modify main menu so it spans the entire page width. I’m hoping there is a simple addition to the custom CSS that would accomplish this. I’ve made other adjustments to the menu background, font color, etc., so the custom CSS under the style tab is as follows:

.header_color .main_menu ul:first-child > li > a { color: #FFFFFF; background-color: #F67736; width:205px; } /* color of main menu items */
.header_color .main_menu ul:first-child > li a:hover { color: #000000; } /* hover state of main menu items */
.header_color .main_menu ul:first-child > li.current-menu-item > a,
.header_color .main_menu ul:first-child > li.current_page_item > a { color: #000000; } /* color of active menu item */
.main_menu .menu li a strong {
display:block;
font-size:12px;
font-weight:normal;
cursor: pointer;
text-align: center; }
#header_meta { display: none; }

.content, .sidebar {
padding-top: 10px;
padding-bottom: 10px;
}

.main_menu ul:first-child > li > a{
display:block;
text-decoration: none;
padding:0 13px;
font-weight: normal;
font-size:12px;
font-weight: 600;
text-align:center;
}

.avia-section-large .content, .avia-section-large .sidebar {
padding-top: 70px;
padding-bottom: 50px;
}
.breadcrumbs { display: none; }

.title_container .main-title {
margin: 0;
font-size: 30px;
font-style: italic;
color: orange;
position: relative;
z-index: 2;
min-height: 36px;
line-height: 2.3em;
top: 0;
font-weight: 400;
}
#top .alternate_color.title_container .main-title a { color:#f05a1a; }