How to add global CSS with my custom app?

Hello, I managed to create and install a custom app with the app sceleton (notes app?).

How would I load a global css file to the theme (or, at least, into the calendar app). Right now, the file /myapp/css/style.css is only included when I open my custom app. I want it to be loaded on all pages of my nextcloud installation.

I included it like that:
myapp/templates/main.php

<?php
    declare(strict_types=1);
    script('myapp', 'script');  // add js/script.js
    style('myapp', 'style');  // add css/style.css
?>

But the files are only loaded when opening the custom app in the menu.

I am already using the app custom css, but this app has limits.
Ultimately, I want to add a custom print.css style to optimize the print output of the calendar and create decent looking PDFs.