I had the same issue. This is how I got it working. It may not be the best way, but it worked for me.
Update the functions.php file for your child theme to include the responsive.css:
function child_enqueue_styles() {
$parent_style = 'parent-style';
wp_enqueue_style( $parent_style, get_template_directory_uri() . '/style.css' );
wp_enqueue_style( $parent_style, get_template_directory_uri() . '/responsive.css' );
wp_enqueue_style( 'child-style',get_stylesheet_directory_uri() . '/custom.css', array( $parent_style ));
}
Then, I had to add the following to custom.css because it wasn’t working for some reason:
@media only screen and (max-width: 992px) {
.mobile_menu_trigger {
display: inline-block;
height: 0;
position: absolute;
right: 0;
top: 38px;
}
}
Hope this helps in some way.