Dark Mode in DCAR for Dotcom and Apps

[JamieB-gu]

The apps support dark mode, so in order for DCR to render articles in the apps it must support dark mode too. Dotcom and Editions do not support dark mode, so DCR components have to include dark mode conditionally, depending on the target currently being rendered for.

How?

We completed a spike on this in #7071 and came up with a proposal for how this might work in #7766. This can be built upon to complete this issue and implement dark mode.

Outstanding Questions

We still need to figure out how to handle "sub-palettes" on articles. While the main content of an article has a single ArticleFormat from which a palette can be derived, the cards in onward content do not and can have a range of different palettes. More information in:

• New Palette Proposal #7766 (comment)
• CSS Variables For Dark Mode #4241 (comment)