Use transform and opacity for animations

Animating layout properties (width, height, top, margin) triggers the full browser rendering pipeline on every frame — style recalculation, layout, paint, and composite. This runs on the main thread and competes with JavaScript. Animating transform and opacity skips layout and paint entirely and runs on a dedicated GPU thread, achieving smooth 60fps even when the main thread is busy.

Quick Reference

• Only transform and opacity can be composited on the GPU without triggering layout
• Use will-change: transform sparingly to promote an element to its own compositor layer
• Prefer CSS transitions and animations over JavaScript animation libraries for simple effects
• Respect prefers-reduced-motion to disable animations for users who need it

Check

Find CSS animations or transitions in this file that animate layout-triggering properties like top, left, width, height, or margin. Flag them for optimization.

Fix

Convert layout-triggering animations to use transform equivalents: position changes to translate(), size changes to scale().