Function
The palette is baked rather than themed. An email cannot read the learner's
stored theme, and cinema-theme-tokens makes dark the variant the product
serves by default, so dark is what the message commits to.
Declaring color-scheme: dark does not stop every client from inverting
it. The Gmail app on iOS inverts every colour but spares background images,
so the fills that must not flip are also painted as one-colour gradients,
and an embedded stylesheet that only Gmail matches blends the light text
back to its colours; the buttons invert as a unit and still read. The same
stylesheet gives the Outlook clients that mark what they re-map with
data-ogsc and data-ogsb the colours to restore. The Outlook app on iOS
honours neither: it re-maps every tinted colour and draws no gradient, so
the dark fills are neutral grays and the glow is also a hosted image.
The shared shape of the account emails, drawn in the Immersion Cinema dark palette: black letterbox bars cropping the cinema gradient into a film frame, and centred between them the wordmark, a heading, one paragraph, one button, the same link printed as text for clients that hide buttons, and a closing line saying what happens if the email is ignored.