[Theme: Twenty Twelve] Change width response from 600px to 760px

I am having problems and I don’t know why, five minutes ago I had this working then it just stopped. I’ve reverted and it still doesn’t work. Anyway I want to change the width, where the mobile view starts, from 600px to 760px so all browsers less than 760px see the mobile menu. I got it working by downloading this version of navigation.js

/**
 * navigation.js
 *
 * Handles toggling the navigation menu for small screens.
 */

jQuery( document ).ready( function( $ ) {
	var masthead = $( '#masthead' ),
		largeWindow = window.matchMedia( 'screen and (min-width: 600px)' ),
		timeout = false;

	$.fn.smallMenu = function() {
		if ( ! masthead.find( '.menu' ).children().length ) {
			$( '.menu-toggle' ).remove();
			return;
		}

		masthead.find( '.site-navigation' ).removeClass( 'main-navigation' ).addClass( 'main-small-navigation' );
		masthead.find( '.site-navigation h3' ).removeClass( 'assistive-text' ).addClass( 'menu-toggle' );

		$( '.menu-toggle' ).off( 'click' ).click( function() {
			masthead.find( '.menu' ).stop().slideToggle();
			$( this ).toggleClass( 'toggled-on' );
		} );
	};

	// Check viewport width on first load.
	if ( ! largeWindow.matches )
		$.fn.smallMenu();

	// Check viewport width when user resizes the browser window.
	$( window ).resize( function() {
		if ( false !== timeout )
			clearTimeout( timeout );

		timeout = setTimeout( function() {
			if ( ! largeWindow.matches ) {
				$.fn.smallMenu();
			} else {
				masthead.find( '.site-navigation' ).removeClass( 'main-small-navigation' ).addClass( 'main-navigation' );
				masthead.find( '.site-navigation h3' ).removeClass( 'menu-toggle' ).addClass( 'assistive-text' );
				masthead.find( '.menu' ).removeAttr( 'style' );
			}
		}, 200 );
	} );
} );

from here https://phpxref.ftwr.co.uk/wordpress/nav.html?wp-content/themes/twentytwelve/js/theme.js.source.html and changed the min-width call in here to 760px and placed this in my css

@media screen and (min-width: 760px) { !important}		/* === Begin 'Mobile View' <=760px; === */

my website is https://www.apalis.co.uk

help would be greatly appreciated, I’m sure I’m missing something small.