Header menu to span entire width of page

I am trying to simply make the menu bar span horizontally across the entire page. For some reason, there is always white space to the left of the menu bar. I would appreciate any help. Thanks!

If it’s helpful: Here are the contents of my custom.css file:
/*Elimate Menu Separator*/
nav.main_menu ul:first-child > li > a{
border: none !important;
}

/*FONT SIZE of Top Menu */
nav.main_menu ul:first-child > li > a{
font-size: 16px !important;
}

/* MENU BAR SPAN ENTIRE PAGE */
#header_main_alternate .container, #header_main_alternate #avia-menu{
width: 100%;

/* SPACE 7 menu ITEMS UNIFORMLY */
}
#header_main_alternate #avia-menu > li{
width: 13.2%; /*(100/7 = 14.29) */
}

/*—- Top Menu Background Color —- */
.header_color nav.main_menu ul li {
background-color: #1B4799 !important;
}