What does unstyled mean?

[zisra]

HeadlessUI describes itself as a collection of unstyled UI components designed to integrate beautifully with Tailwind CSS. What does unstyled mean in this context?
A normal user who is not very proficient would assume that unstyled means "without CSS," (because CSS adds styling).
Obviously, this is not the case. Or does it mean unopinionated? I get how HeadlessUI does not have very strong styling opinions but it still is not what fully unopinionated library would look like.