On my search for an easy to integrate library bringing animating snowflakes to a website - ideally without the need of JS - I've found myself on the wonderful CSSnowflakes library - a lightweight pure CSS solution, only needing you to insert a few lines HTML and the CSS file to your site. Here's a demo page.
To make it even easier to use, without the need of touching Twig templates and theme CSS files, I've wrapped this up in a small Drupal module today: https://www.drupal.org/project/snowflakes
This module is plug & play and ships with two configuration settings currently: one to generally en/disable the snowflakes, and another one to hide it on admin pages.
Hi, at the moment this is not planned... however, please feel free to file any issues, feature requests, patches,... against the issue queue at drupal.org