Initiate the secondary mobile menu at your desired width

gistfile1.txt

@media (max-width: 768px) {
	.menu-toggle,
	.secondary-navigation.toggled .main-nav > ul {
		display: block;
	}
	
	.secondary-navigation ul li.sfHover > ul {
		display: none;
	}
	
	button.menu-toggle {
		background-color: transparent;
		width: 100%;
		border: 0;
	}
	
	button.menu-toggle:hover,
	button.menu-toggle:active,
	button.menu-toggle:focus {
		background-color: transparent;
		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;
	}

	.secondary-navigation ul {
		display: none;
	}
	
	.nav-float-right .secondary-navigation,
	.nav-float-left .secondary-navigation {
		float: none;
		margin-bottom:20px;
	}
	
	.menu-toggle {
		text-align: center;
	}
	
	.main-nav .sf-menu > li {
		float: none;
		clear: both;
	}
	
	.nav-aligned-right.nav-below-header .secondary-navigation .sf-menu > li, 
	.nav-aligned-right.nav-above-header .secondary-navigation .sf-menu > li, 
	.nav-aligned-center.nav-below-header .secondary-navigation .sf-menu > li, 
	.nav-aligned-center.nav-above-header .secondary-navigation .sf-menu > li {
		display: block;
		margin: 0;
		text-align: left;
	}
	
	.secondary-navigation .main-nav ul ul {
		position: relative;
		top: 0;
		left: 0;
		width: 100%;
	}
	
	.menu-item-has-children .dropdown-menu-toggle {
		float: right;
	}
	
	.secondary-navigation {
		text-align:left;
	}
}