Breakpoints (min-width)
sm 640px, md 768px, lg 1024px, xl 1280px, 2xl 1536px. Use as prefix: md:text-lg, lg:grid-cols-3. Mobile-first: base styles, then sm:, md:, etc.
Container and max-*
container centers and sets max-width at breakpoints. max-sm:, max-md: etc. apply below that width. @container for container queries (wrap in @layer).