Note that this is only applied on date-input and not the old date-picker for now.
This commit is also slightly modifying admin report dates form to ensure the native picker is correctly used, as a result: it doesn’t auto refresh on date change and fixes a border bug.
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.
