:root { --w: 720px; font: 16px/1.6 system-ui, -apple-system, Segoe UI, Roboto, sans-serif; }
* { box-sizing: border-box; }
body { margin: 0; padding: 2rem; }
main { max-width: var(--w); margin: 0 auto; }
h1 { line-height: 1.2; margin: 0 0 .5rem; }
nav a { margin-right: .5rem; }
section { margin: 2rem 0; }