:root {
  --bg: #f8fafc;
  --surface: #ffffff;
  --text: #0f172a;
  --muted: #475569;
  --line: #cbd5e1;
  --accent: #0f172a;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.55;
}

.container {
  width: min(860px, 92vw);
  margin: 0 auto;
}

header {
  border-bottom: 1px solid var(--line);
  background: var(--surface);
}

.header-inner {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 16px;
  padding: 16px 0;
}

.brand {
  font-size: 1.1rem;
  font-weight: 650;
  letter-spacing: 0.02em;
}

nav {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
}

nav a {
  color: var(--text);
  text-decoration: none;
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 6px 10px;
  font-size: 0.95rem;
}

nav a:hover {
  border-color: var(--text);
}

main {
  padding: 28px 0 44px;
}

.card {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 20px;
  margin-bottom: 14px;
}

h1 {
  margin: 0 0 10px;
  font-size: clamp(1.55rem, 3vw, 2rem);
}

h2 {
  margin: 24px 0 10px;
  font-size: 1.15rem;
}

h3 {
  margin: 16px 0 8px;
  font-size: 1rem;
}

p {
  margin: 8px 0;
}

ul {
  margin: 8px 0;
  padding-left: 20px;
}

a {
  color: var(--accent);
}

small,
.muted {
  color: var(--muted);
}

footer {
  padding: 20px 0 34px;
  color: var(--muted);
  font-size: 0.92rem;
}

@media (max-width: 640px) {
  .header-inner {
    align-items: flex-start;
    flex-direction: column;
  }
}