Load stylesheet on custom admin submenu page

Question

I'm trying to load a stylesheet for a particular admin submenu page. The code below is what I came up with after looking up admin_enqueue_scripts in the codex:

function my_function($hook) {
    if ( 'themes.php?page=page-name' != $hook ) {
        return;
    }
    wp_enqueue_style( 'custom-style', get_template_directory_uri() . 'custom-page/style.css' );
}
add_action( 'admin_enqueue_scripts', 'my_function' );

As you can see I'm trying to load it on a submenu page. Not just on 'themes.php', but on a custom page I've created called 'page-name'. The code works if 'themes.php' != $hook and loads on 'themes.php'. 'themes.php?page=page-name' != $hook however does not load on 'themes.php?page=page-name'.

Any idea on how to go about this? Thanks in advance!

EDIT: This is how the page is declared

function my_function_settings_page_init() {
    $theme_data = wp_get_theme();
    $settings_page = add_theme_page( $theme_data->get( 'Name' ). ' About', $theme_data->get( 'Name' ). ' About', 'edit_theme_options', 'page-name', 'my_function_settings_page' );
    add_action( "load-{$settings_page}", 'my_function_load_settings_page' );
}

function my_function_load_settings_page() {
    $_POST["my-function-settings-submit"] = '';
    if ( $_POST["my-function-settings-submit"] == 'Y' ) {
        check_admin_referer( "my-function-settings-page" );
        my_function_save_theme_settings();
        $url_parameters = isset($_GET['tab'])? 'updated=true&tab='.$_GET['tab'] : 'updated=true';
        wp_redirect(admin_url('themes.php?page=page-name&'.$url_parameters));
    exit;
    }
}

Answer 1

Ok, I figured it out: If it's a submenu page, the $hook looks like this: appearance_page_page-name instead of going by URL. So the complete code would be this:

function my_function($hook) {
    if ( 'appearance_page_page-name' != $hook ) {
        return;
    }
    wp_enqueue_style( 'custom-style', get_template_directory_uri() . 'custom-page/style.css' );
}
add_action( 'admin_enqueue_scripts', 'my_function' );

Answer 2

if you have declared the page with add_theme_page(..., you can add the stylesheet in the hook load-appearance_page_page-name or admin_print_styles-appearance_page_page-name.

for information, these are some hook which are fired when you load the page (it's not the whole list but the most interesting for your question)

plugins_loaded
init
admin_init
current_screen
load-appearance_page_page-name
admin_enqueue_scripts
admin_print_styles-appearance_page_page-name
admin_print_styles
admin_print_scripts-appearance_page_page-name
admin_print_scripts
wp_print_scripts
admin_head-appearance_page_page-name
admin_head
admin_notices
all_admin_notices
appearance_page_page-name
in_admin_footer
admin_footer-appearance_page_page-name

they are in the order that they append