The scrollbar as a timeline. Scrubbing a transition with the wheel instead of playing it on a timer is what separates a site that responds from a site that merely animates — and it is where most of the cost hides.
Each section sticks at the top and the next one climbs over it. The one underneath is never pushed — it is covered, dimmed and pushed back 6%, which is what makes a stack read as depth instead of as a list.
Flick the row sideways and it settles exactly on the next item. Four CSS declarations, no JavaScript — and the browser keeps its own momentum physics, which is why a hand-written version never feels quite right.
Panels sit on a cylinder around the viewer and scroll rotates the ring. Each panel's place is set once at build time, so the per-frame cost is a single rotation on the parent.
Scroll scrubs between full-bleed scenes: the outgoing panel rotates away in 3D as the next one swings in, with the caption cross-fading rather than being rewritten.
Scroll opens a small card out to full bleed. The card never scales — the window cut out of it does — so the artwork and type inside stay pixel-exact the whole way.