It’s completely flexible. However, it's not done through CSS. We use Typst to generate PDFs, and we template Typst files using Jinja2 from YAML. You can override the built-in Typst templates; see the guide here: https://docs.rendercv.com/user_guide/how_to/override_default...
Ah makes sense, using Typst under the hood for strict layout control compared to CSS. Thanks for the link to the override guide and I'll check it out.