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

body {
  font-family: 'Segoe UI', Arial, sans-serif;
  background: #f0f4f8;
  color: #222;
  padding-bottom: 60px;
}

header {
  background: linear-gradient(135deg, #1a73e8, #0d47a1);
  color: white;
  text-align: center;
  padding: 40px 20px 30px;
}

header h1 {
  font-size: 2.2rem;
  margin-bottom: 8px;
}

header p {
  font-size: 1.05rem;
  opacity: 0.88;
}

.progress-bar-wrap {
  background: rgba(255,255,255,0.25);
  border-radius: 20px;
  height: 12px;
  max-width: 400px;
  margin: 18px auto 0;
  overflow: hidden;
}

.progress-bar {
  background: #ffeb3b;
  height: 100%;
  width: 0%;
  border-radius: 20px;
  transition: width 0.5s ease;
}

.progress-label {
  color: #ffeb3b;
  font-size: 0.9rem;
  margin-top: 6px;
  text-align: center;
}

nav {
  background: #1565c0;
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 6px;
  padding: 12px 16px;
  position: sticky;
  top: 0;
  z-index: 100;
}

nav a {
  color: #e3f2fd;
  text-decoration: none;
  font-size: 0.8rem;
  padding: 4px 10px;
  border-radius: 12px;
  background: rgba(255,255,255,0.12);
  transition: background 0.2s;
}

nav a:hover {
  background: rgba(255,255,255,0.28);
}

main {
  max-width: 900px;
  margin: 30px auto;
  padding: 0 16px;
  display: flex;
  flex-direction: column;
  gap: 32px;
}

.rule-card {
  background: white;
  border-radius: 16px;
  box-shadow: 0 4px 18px rgba(0,0,0,0.09);
  overflow: hidden;
}

.rule-header {
  padding: 20px 24px 16px;
  color: white;
}

.rule-header .rule-num {
  font-size: 0.85rem;
  opacity: 0.8;
  margin-bottom: 2px;
}

.rule-header h2 {
  font-size: 1.4rem;
  margin-bottom: 2px;
}

.rule-header h3 {
  font-size: 1rem;
  font-weight: 400;
  opacity: 0.9;
}

.rule-body {
  padding: 20px 24px;
}

.explain-box {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin-bottom: 18px;
}

@media (max-width: 600px) {
  .explain-box {
    grid-template-columns: 1fr;
  }
  header h1 { font-size: 1.5rem; }
}

.explain-lv {
  background: #e8f5e9;
  border-left: 4px solid #43a047;
  padding: 12px 14px;
  border-radius: 8px;
  font-size: 0.95rem;
  line-height: 1.6;
}

.explain-en {
  background: #e3f2fd;
  border-left: 4px solid #1e88e5;
  padding: 12px 14px;
  border-radius: 8px;
  font-size: 0.95rem;
  line-height: 1.6;
}

.explain-lv strong, .explain-en strong {
  display: block;
  margin-bottom: 5px;
  font-size: 0.82rem;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  opacity: 0.65;
}

.examples {
  background: #fafafa;
  border-radius: 10px;
  padding: 14px 18px;
  margin-bottom: 20px;
}

.examples h4 {
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  color: #888;
  margin-bottom: 10px;
}

.example-row {
  display: flex;
  gap: 10px;
  margin-bottom: 6px;
  align-items: flex-start;
  flex-wrap: wrap;
}

.example-row .lv {
  flex: 1;
  min-width: 140px;
  color: #2e7d32;
  font-size: 0.93rem;
}

.example-row .en {
  flex: 1;
  min-width: 140px;
  color: #1565c0;
  font-weight: 600;
  font-size: 0.93rem;
}

.arrow {
  color: #bbb;
  font-size: 1.1rem;
  padding-top: 1px;
}

/* TEST SECTION */
.test-section {
  border-top: 2px dashed #e0e0e0;
  padding-top: 18px;
}

.test-section h4 {
  font-size: 1rem;
  margin-bottom: 14px;
  color: #333;
}

.quiz-question {
  margin-bottom: 18px;
}

.quiz-question p {
  font-size: 0.95rem;
  margin-bottom: 8px;
  font-weight: 500;
}

.options {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.option-btn {
  background: #f5f5f5;
  border: 2px solid #e0e0e0;
  border-radius: 8px;
  padding: 9px 14px;
  text-align: left;
  cursor: pointer;
  font-size: 0.9rem;
  transition: all 0.2s;
}

.option-btn:hover:not(:disabled) {
  background: #e3f2fd;
  border-color: #90caf9;
}

.option-btn.correct {
  background: #e8f5e9;
  border-color: #43a047;
  color: #1b5e20;
}

.option-btn.wrong {
  background: #ffebee;
  border-color: #e53935;
  color: #b71c1c;
}

.feedback {
  font-size: 0.88rem;
  margin-top: 6px;
  min-height: 20px;
  font-weight: 500;
}

.feedback.ok { color: #2e7d32; }
.feedback.fail { color: #c62828; }

.score-box {
  background: #fff3e0;
  border: 2px solid #ff9800;
  border-radius: 10px;
  padding: 12px 16px;
  margin-top: 16px;
  font-size: 0.95rem;
  text-align: center;
  display: none;
}

.score-box.show { display: block; }

/* Color themes */
.c1 .rule-header { background: linear-gradient(135deg,#e53935,#b71c1c); }
.c2 .rule-header { background: linear-gradient(135deg,#8e24aa,#6a1b9a); }
.c3 .rule-header { background: linear-gradient(135deg,#1e88e5,#0d47a1); }
.c4 .rule-header { background: linear-gradient(135deg,#00897b,#004d40); }
.c5 .rule-header { background: linear-gradient(135deg,#f4511e,#bf360c); }
.c6 .rule-header { background: linear-gradient(135deg,#3949ab,#1a237e); }
.c7 .rule-header { background: linear-gradient(135deg,#00acc1,#006064); }
.c8 .rule-header { background: linear-gradient(135deg,#7cb342,#33691e); }
.c9 .rule-header { background: linear-gradient(135deg,#f9a825,#e65100); }
.c10 .rule-header { background: linear-gradient(135deg,#d81b60,#880e4f); }
.c11 .rule-header { background: linear-gradient(135deg,#546e7a,#263238); }
.c12 .rule-header { background: linear-gradient(135deg,#6d4c41,#3e2723); }

footer {
  text-align: center;
  padding: 30px 20px;
  color: #888;
  font-size: 0.85rem;
}

@media (max-width: 768px) {
  header {
    padding: 28px 14px 22px;
  }

  header h1 {
    font-size: 1.6rem;
    line-height: 1.25;
  }

  nav {
    justify-content: flex-start;
    flex-wrap: nowrap;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
    padding: 10px 12px;
  }

  nav a {
    flex: 0 0 auto;
    font-size: 0.85rem;
    padding: 8px 12px;
  }

  .rule-body {
    padding: 16px 14px;
  }

  .rule-header {
    padding: 16px 14px 14px;
  }
}