Hi Ajjet,
Just follow the instructions, everything is described in detail https://getpublii.com/docs/highlight-your-code-syntax-with-prism-js.html
Your example does not contain the prism.js file, this one must be added to the footer section. To have a popup with a list of coding languages you have to add them to the config.json file.
The” dark layout” was created by me and is available and delivered only with the following themes: Documentation and ProDocs.