* { box-sizing:border-box; }
body { margin:0; font:15px/1.65 "Segoe UI",Arial,sans-serif; color:#24292e; background:#fff; }
header, main, footer { max-width:680px; margin:0 auto; padding:1rem 1.25rem; }
header { border-bottom:2px solid #24292e; display:flex; justify-content:space-between; align-items:baseline; flex-wrap:wrap; gap:.5rem; }
h1 { font-size:1.25rem; margin:0; letter-spacing:.02em; }
nav a { margin-left:.9rem; color:#0366d6; text-decoration:none; }
footer { border-top:1px solid #e1e4e8; color:#6a737d; }