Code highlighter on website

Hello,

Building my own theme.
When testing a code-block doesn’t work.
After searching founding and adding this solution:
https://prismjs.com/

Works great, only…
When looking in my source code seeing some code snippetswith this css-class:
jekyll serve

Found that this is a Ruby plugin?
Okay, try adding in _config.yml:
highlighter: rouge

Read also this docs, but can’ find how implement Jekyll’s ‘default’ code-hightlighter:

I’m new with Jekyll, so i missing something?

the css for highlighting is usually something you have to add yourself - rouge will create all the classes, but if you don’t have the css for those classes nothing will happen.

here is a link to one example of the css that would probably work:

Adding the css to my website, that works perfect!!!