Initiate the mobile menu at your desired width

gistfile1.css

@media (max-width: 768px) {
	.menu-toggle,
	.main-navigation.toggled .main-nav > ul {
		display: block;
	}
	
	.main-navigation ul li.sfHover > ul,
	.main-navigation ul {
		display: none;
	}
	
	.main-navigation .menu li.search-item {
		display: none !important;
	}
	
	button.menu-toggle,
	button.menu-toggle:hover,
	button.menu-toggle:active,
	button.menu-toggle:focus {
		background-color: transparent;
		width: 100%;
		border: 0;
		outline: 0;
	}
	
	.sub-menu.toggled-on,
	.children.toggled-on {
		display: block !important;
		opacity: 1 !important;
	}
	
	.dropdown-menu-toggle:before {
		content: "\f107" !important;
	}
	
	.sfHover > a .dropdown-menu-toggle:before {
		content: "\f106" !important;
	}
	
	[class*="nav-float-"] .site-header .inside-header > * {
		float: none;
		clear: both;
	}
	
	.inside-header > *:not(:last-child) {
		margin-bottom: 20px;
	}
	
	.mobile-bar-items {
		display: block;
		position: absolute;
		right: 0;
		top: 0;
		z-index: 21;
		list-style-type: none;
	}
	
	.mobile-bar-items a {
		display: inline-block;
	}
	
	.menu-toggle {
		text-align: center;
	}
	
	.nav-search-enabled .main-navigation .menu-toggle {
		text-align: left;
	}
	
	.main-nav .sf-menu > li {
		float: none;
		clear: both;
	}
	
	.nav-aligned-right.nav-below-header .main-navigation .sf-menu > li, 
	.nav-aligned-right.nav-above-header .main-navigation .sf-menu > li, 
	.nav-aligned-center.nav-below-header .main-navigation .sf-menu > li, 
	.nav-aligned-center.nav-above-header .main-navigation .sf-menu > li {
		display: block;
		margin: 0;
		text-align: left;
	}
	
	.main-navigation .main-nav ul ul {
		position: relative;
		top: 0;
		left: 0;
		width: 100%;
	}
	
	.menu-item-has-children .dropdown-menu-toggle {
		float: right;
	}
	
	.main-navigation {
		text-align:left;
	}
	
	.sf-menu > li.menu-item-float-right {
		float: none !important;
		display: inline-block;
	}
}