Document how gitlab-ui interacts with gitlab CSS
Problem
When we introduced color changes to gitlab-ui, the variables overrode GitLab color variables in multiple places.
We then updated gitlab-ui to mark them with !default
so that GitLab overrides the variables and bumped the gitlab-ui version in gitlab to essentially revert the color changes (gitlab!28049 (merged)).
It wasn't clear to us at the time that the GitLab CSS would not override the gitlab-ui variable changes. It would be helpful to have more information on relationship between gitlab SCSS and gitlab-ui SCSS. We should document this somewhere so that new members who join the team can also understand the relationship (esp when we are in the state where variables are in both gitlab and gitlab-ui).
We also want to clearly articulate the timeframe for once something is merged in gitlab-ui, how long does it take for the version to be pumped in gitlab, deployed to canary, and then to production?