Refreshed design.
Refreshed design.

Summary:
This is #12292, but squashed into a single commit. This should help land the PR cleanly, as the commit history for #12292 was in a bad state: see how 1cbf79d456172c1d348a925d32a7f817df4aaf4b expects `"mkdirp": "^0.5.1"` in `package.json`, but the earlier 66920e4e4b04174d63834d6220c4da76453f27a2 had changed this to `"mkdirp": "*",`.

Verified the website built and run.
Confirmed docs, apis, components were generated.
Confirmed landing page, showcase, blog, docs, help page all load and look as expected.
Closes https://github.com/facebook/react-native/pull/12575

Differential Revision: D4617979

Pulled By: hramos

fbshipit-source-id: 86e2d0b36ccd25fc7f2e9f3b1351f97e7ba64d57

ankitsinghania94/react-native,ankitsinghania94/react-native,ankitsinghania94/react-native,ankitsinghania94/react-native,ankitsinghania94/react-native,ankitsinghania94/react-native,ankitsinghania94/react-native,ankitsinghania94/react-native