A first step to adding automatic dark mode color scheme switching. Adds a new SCSS file at `color_definitions.scss` that serves to output all SCSS color variables as CSS custom properties. And replaces all SCSS color variables with the new CSS custom properties throughout the stylesheets.
This is an alpha feature at this point, can only be enabled via console using the `default_dark_mode_color_scheme_id` site setting.
If you click a (?) icon beside the reviewable status a pop up will
appear with expanded informatio that explains how the reviewable got its
score, and how it compares to system thresholds.
Penar Musaraj
Robin Ward