* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  background: #f9f9f9;
  color: #333;
  line-height: 1.7;
}

.site-header {
  background: white;
  padding: 1.5rem 2rem;
  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.06);
  position: sticky;
  top: 0;
}

.site-header h1 {
  font-size: 1.5rem;
  margin-bottom: 0.5rem;
}

nav a {
  margin-right: 1rem;
  color: #2563eb;
  text-decoration: none;
}

nav a:hover {
  text-decoration: underline;
}

main {
  max-width: 960px;
  margin: 0 auto;
  padding: 2rem 1rem;
}

.hero {
  background: linear-gradient(135deg, #e0f2fe, #f0f9ff);
  padding: 2rem;
  border-radius: 16px;
  margin-bottom: 2rem;
}

.hero h2 {
  font-size: 2rem;
  margin-bottom: 0.5rem;
}

.section {
  margin-bottom: 2.5rem;
}

.section h2 {
  font-size: 1.5rem;
  margin-bottom: 1rem;
}

.word-card {
  background: white;
  border-radius: 16px;
  padding: 2rem;
  text-align: center;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
  max-width: 420px;
}

.word {
  font-size: 2.5rem;
  font-weight: 700;
  color: #1e3a8a;
}

.phonetic {
  color: #64748b;
  margin: 0.5rem 0 1rem;
}

.meaning {
  background: #f1f5f9;
  border-radius: 12px;
  padding: 1rem;
  margin: 1rem 0;
  text-align: left;
}

.hidden {
  display: none;
}

button {
  background: #2563eb;
  color: white;
  border: none;
  padding: 0.7rem 1.5rem;
  border-radius: 999px;
  cursor: pointer;
  font-size: 1rem;
}

button:hover {
  background: #1d4ed8;
}

.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 1rem;
}

.card {
  background: white;
  border-radius: 12px;
  padding: 1.5rem;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.06);
}

.card h3 {
  margin-bottom: 0.5rem;
}

footer {
  text-align: center;
  padding: 2rem;
  color: #64748b;
  font-size: 0.9rem;
}