Previously the grain lived on .page-texture's own background-image, so
any section with its own opaque background color (bg-neutral-50 bands)
painted right over it. Moved the grain to a fixed, full-viewport overlay
that sits on top of everything instead.
Also fixed a failed attempt at using mix-blend-mode: overlay for a
single theme-agnostic texture - that blend mode has almost no visible
effect on backgrounds this close to pure white/black, since its math
compresses toward the backdrop at the extremes. Back to plain alpha
transparency with separate light/dark speckle colors, moderate opacity.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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