Are blog pages able to be customised?

Yes, although I don't see many people using it. Few people use CSS, and the people who aren't dummies skip using SpaceHey generic default editor and write their blogs on other sites, then copy and paste the content here (keeping the format, of course).

EDIT: Oh look, this was posted shortly after my comment. Convenient, isn't it?

https://blog.spacehey.com/entry?id=855912

So if I was to change my journal would it only be compatible with css and not html? And thank you so much! I’ll definitely look into coding my own :D