[Theme Horse Support Team]

Hi Sam,

If you write any Css in Custom CSS then nothing will be lost while updating to our new version. To enqueue responsive css Just add this below code.

// Unhook default Thematic functions
function unhook_thematic_functions() {
    // Don't forget the position number if the original function has one
remove_action( 'wp_enqueue_scripts', 'interface_scripts_styles_method'); // for responsive.css
}
add_action('init','unhook_thematic_functions'); // removes the header content by using hook interface_header
add_action( 'wp_enqueue_scripts', 'wp_enqueue_child_scripts');
function wp_enqueue_child_scripts() {
	global $interface_theme_default;
   $options = $interface_theme_default;

   /**
	 * Loads our main stylesheet.
	 */
	// Load our main stylesheet.
	wp_enqueue_style( 'parent-style', get_template_directory_uri() . '/style.css' );
	wp_enqueue_style( 'child-style', get_stylesheet_uri(), array( 'parent-style' ) );
	
	wp_style_add_data( 'interface-ie', 'conditional', 'lt IE 9' ); 
	
	if ('on' == $options['site_design']) {
	//Css for responsive design
	wp_enqueue_style( 'interface-responsive', get_template_directory_uri() . '/css/responsive.css');
	wp_enqueue_style( 'interface-child-responsive', get_stylesheet_directory_uri() . '/css/responsive.css' );
	}
	/**
	 * Adds JavaScript to pages with the comment form to support
	 * sites with threaded comments (when in use).
	 */
	if ( is_singular() && comments_open() && get_option( 'thread_comments' ) )
		wp_enqueue_script( 'comment-reply' );

	/**
	 * Register JQuery cycle js file for slider.
	 * Register Jquery fancybox js and css file for fancybox effect.
	 */
	wp_register_script( 'jquery_cycle', INTERFACE_JS_URL . '/jquery.cycle.all.min.js', array( 'jquery' ), '2.9999.5', true );

   wp_register_style( 'google_fonts', '//fonts.googleapis.com/css?family=PT+Sans:400,700italic,700,400italic&subset=latin,cyrillic-ext,latin-ext' ); 

	
	/**
	 * Enqueue Slider setup js file.
	 * Enqueue Fancy Box setup js and css file.	 
	 */	
	if( ( is_home() || is_front_page() ) && "0" == $options[ 'disable_slider' ] ) {
		wp_enqueue_script( 'interface_slider', INTERFACE_JS_URL . '/interface-slider-setting.js', array( 'jquery_cycle' ), false, true );
	}
  
	wp_enqueue_script( 'backtotop', INTERFACE_JS_URL. '/backtotop.js', array( 'jquery' ) );
	wp_enqueue_script( 'scripts', INTERFACE_JS_URL. '/scripts.js', array('jquery') );

   wp_enqueue_style( 'google_fonts' );

}

Create the child theme folder-> css folder -> (responsive.css) and edit it in you own way.
and under style.css use this below code only

/*
Theme Name: interface Child Theme
Author: Self-Help WordPress User
Template: interface
*/

Thank you!