User specific CSS for WordPress admin

Add this snippet to functions.php

function add_css_to_guest_user() {
    $guest_user = wp_get_current_user();

    if($guest_user && isset($guest_user->user_login) && 'guest' == $guest_user->user_login) {
        wp_enqueue_style( 'guest_admin_css', get_stylesheet_directory_uri() . '/css/wpadmin-guest.css' );
    }
}
add_action('admin_print_styles', 'add_css_to_guest_user' );

2) CSS

If You want to hide the CF7 menu item on guest user’s WordPress admin use this CSS

#toplevel_page_wpcf7 {
	display: none;
}