Description markdown missing CSS for headings

What the editor looks like:
<img width="381" alt="image" src="https://github.com/barthuijgen/factorio-sites/assets/1266923/f13db6a0-764d-4faf-997a-ecc10ac78bf8">

What the details page looks like
<img width="570" alt="image" src="https://github.com/barthuijgen/factorio-sites/assets/1266923/af1e91aa-6c3d-4327-a232-ebca1aa71fb9">

Looks like we're missing some CSS for the rendered description.