Custom Post Types – How to include custom fields

@vemuez

you need to enqueue js and css files to admin_print_script and admin_print_style

here is the example to how to do it

// Register datepicker ui for properties

function admin_homes_for_sale_javascript()
{
    global $post;
    if($post->post_type == 'homes-for-sale' && is_admin()) {
        wp_enqueue_script('jquery-ui-datepicker', WP_CONTENT_URL . '/themes/yourthemename/js/jquery-ui-datepicker.min.js');  
    }
}
add_action('admin_print_scripts', 'admin_homes_for_sale_javascript');

// Register ui styles for properties

function admin_homes_for_sale_styles(){
    global $post;
    if($post->post_type == 'homes-for-sale' && is_admin()) {
        wp_enqueue_style('jquery-ui', WP_CONTENT_URL . '/themes/yourthemename/css/jquery-ui-1.8.11.custom.css');  
    }
}
add_action('admin_print_styles', 'admin_homes_for_sale_styles');

or try this
https://en.bainternet.info/how-i-add-a-wordpress-metabox/#toc-dn