:root {
  --bg: #f7f7fb;
  --card: #ffffff;
  --text: #1f2937;
  --muted: #6b7280;
  --border: #e5e7eb;
  --accent: #2563eb;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Arial, Helvetica, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
}

header {
  background: #111827;
  color: white;
  padding: 40px 20px;
  text-align: center;
}

header h1 {
  margin: 0 0 10px;
  font-size: 2rem;
}

header p {
  margin: 0;
  color: #d1d5db;
}

nav {
  background: white;
  border-bottom: 1px solid var(--border);
  padding: 12px 20px;
  text-align: center;
  position: sticky;
  top: 0;
}

nav a {
  color: var(--accent);
  text-decoration: none;
  margin: 0 10px;
  font-weight: bold;
}

main {
  max-width: 1000px;
  margin: 30px auto;
  padding: 0 20px;
}

.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 22px;
  margin-bottom: 20px;
  box-shadow: 0 2px 10px rgba(0,0,0,0.03);
}

.card h2, .card h3 {
  margin-top: 0;
}

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 16px;
}

.button {
  display: inline-block;
  background: var(--accent);
  color: white;
  padding: 10px 14px;
  border-radius: 10px;
  text-decoration: none;
  font-weight: bold;
  margin-top: 8px;
}

.lesson-list {
  padding-left: 20px;
}

.lesson-list li {
  margin-bottom: 8px;
}

.note {
  color: var(--muted);
  font-size: 0.95rem;
}

.qr-placeholder {
  width: 260px;
  height: 260px;
  border: 2px dashed var(--border);
  border-radius: 16px;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  color: var(--muted);
  background: #fafafa;
  margin: 20px 0;
  padding: 20px;
}

footer {
  text-align: center;
  color: var(--muted);
  padding: 30px 20px;
  font-size: 0.9rem;
}