HTML email dark mode: style both schemes and drop the page background

Outlook for Mac and Apple Mail invert a light-only email into muddy grays (an off-white page background turned dark gray, a beige code box went charcoal). Fix: add meta color-scheme 'light dark', give elements classes with explicit light colors plus a prefers-color-scheme: dark block using !important, and leave the body/outer table without a background so the card sits on the client's own canvas. Keep brand images (header strip, logo on a white rounded tile) self-contained so they read on either background. Gmail ignores these styles and applies its own darkening, so check it separately. Also: a webfont family name like Poppins may resolve to a locally installed heavier weight in Outlook; body text in the system stack with explicit font-weight avoids accidental bold.