:root {
  --canvas: #F4F7FF; --surface: #FFFFFF; --ink: #111827; --subtle: #5B6475;
  --hairline: #DDE3F0; --brand: #2A6BFF; --deep: #1736C9;
}
@media (prefers-color-scheme: dark) {
  :root {
    --canvas: #070B16; --surface: #111827; --ink: #EEF2FF; --subtle: #9AA3B5;
    --hairline: #1F2937; --brand: #5CC8FF; --deep: #0E1B66;
  }
}
* { box-sizing: border-box; }
body {
  margin: 0; background: var(--canvas); color: var(--ink);
  font: 17px/1.6 -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  -webkit-font-smoothing: antialiased;
}
/* Nada de backdrop-filter en una cabecera fija: crea un contexto de composición
   que oscurece toda la página que queda por debajo. */
header {
  background: var(--deep); color: #fff; padding: 56px 20px 44px; text-align: center;
}
header h1 { margin: 0 0 8px; font-size: clamp(30px, 7vw, 44px); letter-spacing: -0.02em; }
header p { margin: 0; opacity: 0.8; font-size: 17px; }
nav { display: flex; gap: 18px; justify-content: center; margin-top: 22px; flex-wrap: wrap; }
nav a { color: #fff; opacity: 0.85; text-decoration: none; border-bottom: 1px solid rgba(255,255,255,.35); padding-bottom: 2px; }
nav a:hover { opacity: 1; }
main { max-width: 720px; margin: 0 auto; padding: 44px 20px 80px; }
h2 { font-size: 24px; margin: 44px 0 12px; letter-spacing: -0.01em; }
h2:first-child { margin-top: 0; }
h3 { font-size: 18px; margin: 28px 0 6px; }
p, li { color: var(--ink); }
.subtle { color: var(--subtle); }
ul { padding-left: 22px; }
li { margin-bottom: 8px; }
.card {
  background: var(--surface); border: 1px solid var(--hairline);
  border-radius: 16px; padding: 20px 22px; margin: 20px 0;
}
a { color: var(--brand); }
footer { border-top: 1px solid var(--hairline); margin-top: 56px; padding-top: 22px; color: var(--subtle); font-size: 14px; }
code { background: var(--hairline); padding: 2px 6px; border-radius: 5px; font-size: 14px; }
@media (prefers-reduced-motion: reduce) { * { transition: none !important; animation: none !important; } }
header img { width: 84px; height: 84px; border-radius: 19px; margin-bottom: 14px; box-shadow: 0 8px 24px rgba(0,0,0,.25); }