The custom CSS for chabadmc.org, served by GitHub Pages at:
https://ari-cmc.github.io/chabadmc-site-styles/chabadmc.css
ChabadOne loads it from Settings → General Settings → Advanced → Custom Header Code with this one line:
<style type="text/css">@import url("https://ari-cmc.github.io/chabadmc-site-styles/chabadmc.css");</style>
Edit chabadmc.css, commit to main, and the live site picks it up within about 10 minutes (GitHub Pages cache). To undo a change, revert its commit.
This repo is public on purpose: browsers only load stylesheets from public addresses, and a website’s CSS is visible to anyone anyway. Put nothing private here.