Summary:
This diff fixes two problems when further theming Flipper:
1. All shades of gray where defined in terms of black/white + transparency. Converted all colors to non transparent to make sure they stack well.
2. The color theme defined in less aren't available as javascript colors. It is possible to achieve that through setting up a babel parser that parses the less files and exposes them to JS. But since we have modern stack, figured that exposing all theme variables as CSS variables as well is a much simpler setup.
Reviewed By: passy
Differential Revision: D23756558
fbshipit-source-id: e92be1f66b11c2c9c400fc1622cb8a493cc4c2a5
694d4e0e33