[Feature request] Make theme updates

[huijing]

Currently the look and feel is exactly the same as /developers. We want to have some visual styles that better fit a learning hub. Will work with Madalina on how this will play out.

Given that this will deviate from the standard documentation styling, it would be better if we made these visual updates in this codebase, rather than introducing a new stylesheet/components to the docs-design-library, since those styles will likely never be shared with another site.