feat: added light mode and dark mode support for codeblocks (#3532)
feat: added light mode and dark mode support for codeblocks (#3532)

Summary:
added light mode support from docusaurus 2.0.0beta.1

earlier:

<img width="1127" alt="image" src="https://user-images.githubusercontent.com/40708551/123577625-ceb52400-d7f1-11eb-8da0-df7ffec24bf2.png">

Now:

https://user-images.githubusercontent.com/40708551/123577718-03c17680-d7f2-11eb-8b6c-7e147c6d2971.mov

<img width="1324" alt="image" src="https://user-images.githubusercontent.com/40708551/123577565-b47b4600-d7f1-11eb-8fc3-abd44cdc4245.png">

Pull Request resolved: https://github.com/facebook/relay/pull/3532

Test Plan:
Imported from GitHub, without a `Test Plan:` line.

|[Site Preview: relay](https://our.intern.facebook.com/intern/staticdocs/eph/D29688390/V2/relay/)

Reviewed By: alunyov

Differential Revision: D29688390

Pulled By: kassens

fbshipit-source-id: c39beb6076d210329b613ba95e926a4d8ef75cad

voideanvalue/relay,facebook/relay,facebook/relay,wincent/relay,voideanvalue/relay,xuorig/relay,josephsavona/relay,xuorig/relay,voideanvalue/relay,xuorig/relay,facebook/relay,josephsavona/relay,facebook/relay,josephsavona/relay,wincent/relay,wincent/relay,kassens/relay,facebook/relay,kassens/relay,kassens/relay,voideanvalue/relay,xuorig/relay,xuorig/relay,wincent/relay,voideanvalue/relay,voideanvalue/relay,kassens/relay,kassens/relay,facebook/relay,xuorig/relay,kassens/relay,wincent/relay,wincent/relay