Best practices for building scroll-driven animations on websites. Use this skill whenever the user asks to create scroll animations, parallax effects, scroll-triggered reveals, scroll progress bars, sticky headers that animate on scroll, fade-in-on-scroll effects, scrollytelling pages, or any animation tied to the user's scroll position. Also trigger when the user mentions GSAP ScrollTrigger, Intersection Observer, CSS scroll-driven animations, animation-timeline, scroll(), view(), Lenis, or scroll-linked motion of any kind. If the user wants elements to animate as they scroll into view, this is the skill to use.