@radfactor, regarding disabling activities from search form. Please add this snippet

add_filter( ‘wp_travel_search_filter_input_fields’, ‘prefix_wp_travel_search_filter_input_fields’ );
function prefix_wp_travel_search_filter_input_fields(){
$filter_search = array(
‘search’ => true,
‘trip_type’ => true,
‘location’ => false,
‘activity’ => false,
‘travel_keywords’ => false,
);
return $filter_search;
}

Here is screen record how to add the snippet
https://www.awesomescreenshot.com/video/34938007?key=18527eda12708141980594c06f7f509b

Regarding “changing font size” – query is quite not clear, is it a shortcode or itinerary page. Could you please share a url of the page?