Paste in the browser the code you want to highlight, select language and theme and get back the code highlighted. No external css needed!
Based on Rouge Ruby syntax highlighter: https://github.com/rouge-ruby/rouge
216 Languages supported!
You can use it online here: https://rouge.fly.dev/
git clone https://github.com/ZioTester/Rouge-Highlighter-Online
cd Rouge-Highlighter-Online
bundle install
puma