On Dark, Borders Beat Shadows
SHOULD: On dark surfaces define elevation with a hairline low-opacity border plus one small step of surface lightness, not a drop shadow — a shadow works by darkening pixels behind the element and near-black has no luminance left to remove, so `shadow-lg` exists in the computed style and nowhere on screen.
Define elevation on dark surfaces with a hairline border and a surface lightness step, because a drop shadow has nothing left to darken
Bad
Good
Why it matters
A drop shadow works by darkening the pixels behind an element. On a near-black background there is almost no luminance left to remove, so shadow-lg on a dark card produces an elevation that exists in the computed style and nowhere on the screen — and if the card fill matches the panel behind it, the edges disappear entirely. Definition on dark comes from two cheaper, more reliable levers: a hairline border (a low-opacity light stroke reads as a crisp edge at any ambient brightness) and one small step of surface lightness — each jump only a few percentage points, barely visible in isolation but unmistakable once stacked.
This is distinct from two neighbours in this corpus. design-impeccable-dark-glow is about the opposite failure — a saturated chroma glow spilling off a dark card, which is loud but meaningless. content-impeccable-dark-mode-text-compensation is about the type on dark (weight and colour compensation), not the box around it. This principle is only about where the edge of the box comes from.