:root {
  --primary: #2b6cb0;
  --bg: #f7f9fc;
  --card-bg: #ffffff;
  --border: #dfe6ee;
  --text: #1a202c;
  --muted: #5a6472;
}
* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
}
header {
  background: linear-gradient(135deg, #2b6cb0, #234e8c);
  color: #fff;
  padding: 2rem 1.5rem 1.5rem;
  text-align: center;
}
header h1 { margin: 0 0 .3rem; font-size: 1.9rem; }
.subtitle { margin: 0 0 1rem; opacity: .9; font-size: .95rem; }
.state-select { display: inline-flex; gap: .5rem; align-items: center; background: rgba(255,255,255,.15); padding: .5rem 1rem; border-radius: 8px; }
.state-select select { padding: .3rem .5rem; border-radius: 6px; border: none; font-size: 1rem; }

#mainNav {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: .5rem;
  padding: 1rem;
  background: #fff;
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 10;
}
.nav-btn {
  background: none;
  border: 2px solid var(--border);
  padding: .6rem 1.1rem;
  border-radius: 999px;
  font-size: .95rem;
  cursor: pointer;
  color: var(--muted);
  transition: all .15s;
}
.nav-btn:hover { border-color: var(--primary); color: var(--primary); }
.nav-btn.active { background: var(--primary); border-color: var(--primary); color: #fff; }

main { max-width: 900px; margin: 0 auto; padding: 1.5rem; }
.tab-content { display: none; }
.tab-content.active { display: block; }
h2 { color: var(--primary); border-bottom: 2px solid var(--border); padding-bottom: .4rem; }

.card-group { display: flex; flex-direction: column; gap: 1rem; margin-top: 1rem; }
.card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1.1rem 1.3rem;
  box-shadow: 0 1px 3px rgba(0,0,0,.04);
}
.card h3 { margin-top: 0; color: #1a365d; }
.card h4 { margin-bottom: .3rem; color: var(--primary); }
.card ul { padding-left: 1.2rem; }
.tag {
  display: inline-block;
  background: #ebf4ff;
  color: var(--primary);
  font-size: .78rem;
  padding: .15rem .55rem;
  border-radius: 999px;
  margin-bottom: .5rem;
  font-weight: 600;
}
.muted { color: var(--muted); font-size: .88rem; }
.klassen-select { margin: 1rem 0; }
.klassen-select select { padding: .4rem .6rem; border-radius: 6px; border: 1px solid var(--border); font-size: 1rem; }
.aufgabe { border-left: 3px solid var(--primary); padding-left: .8rem; margin: .6rem 0; }
.aufgabe .frage { font-weight: 600; }
.aufgabe .loesung { color: var(--muted); }
details summary { cursor: pointer; color: var(--primary); font-weight: 600; }
.two-col { display: flex; gap: 1.5rem; flex-wrap: wrap; }
.two-col > div { flex: 1; min-width: 220px; }
footer { text-align: center; padding: 1.5rem; color: var(--muted); font-size: .8rem; }