* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

body {
  background-color: #f0f4f8;
  color: #333;
  display: flex;
  justify-content: center;
}

.app-container {
  width: 100%;
  max-width: 480px; /* Batas lebar tampilan layar HP */
  min-height: 100vh;
  background-color: #ffffff;
  box-shadow: 0 0 15px rgba(0,0,0,0.1);
  display: flex;
  flex-direction: column;
}

.header {
  background: linear-gradient(135deg, #4A90E2, #007AFF);
  color: white;
  text-align: center;
  padding: 20px 15px;
}

.header h1 {
  font-size: 1.5rem;
  margin-bottom: 5px;
}

.header p {
  font-size: 0.9rem;
  opacity: 0.9;
}

.nav-menu {
  display: flex;
  background-color: #e1e8f0;
  border-bottom: 2px solid #ccc;
}

.nav-btn {
  flex: 1;
  padding: 12px 5px;
  border: none;
  background: none;
  font-size: 0.9rem;
  font-weight: bold;
  color: #555;
  cursor: pointer;
  transition: 0.3s;
}

.nav-btn.active {
  background-color: #ffffff;
  color: #007AFF;
  border-bottom: 3px solid #007AFF;
}

.content {
  padding: 15px;
  flex: 1;
}

.tab-content {
  display: none;
}

.tab-content.active {
  display: block;
}

.card {
  background-color: #ffffff;
  border-radius: 12px;
  padding: 15px;
  margin-bottom: 15px;
  border: 1px solid #e1e8f0;
  box-shadow: 0 2px 5px rgba(0,0,0,0.05);
}

.card h2 {
  font-size: 1.1rem;
  color: #007AFF;
  margin-bottom: 10px;
}

.card p {
  font-size: 0.95rem;
  line-height: 1.4;
}

.formula-box, .example-box, .result-box {
  background-color: #eef6ff;
  border-left: 4px solid #007AFF;
  padding: 12px;
  border-radius: 6px;
  margin: 10px 0;
  text-align: center;
}

.formula-box p {
  font-size: 1.1rem;
}

.input-group {
  margin: 15px 0;
}

.input-group label {
  display: block;
  margin-bottom: 5px;
  font-weight: bold;
}

.input-group input {
  width: 100%;
  padding: 10px;
  border: 1px solid #ccc;
  border-radius: 8px;
  font-size: 1rem;
  text-align: center;
}

/* Kuis Style */
.quiz-header {
  font-size: 0.85rem;
  color: #777;
  margin-bottom: 8px;
}

.question {
  font-weight: bold;
  font-size: 1rem;
  margin-bottom: 15px;
}

.options-group {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.option-btn {
  padding: 12px;
  border: 1px solid #007AFF;
  background-color: #fff;
  color: #007AFF;
  border-radius: 8px;
  font-size: 0.95rem;
  text-align: left;
  cursor: pointer;
  transition: 0.2s;
}

.option-btn.correct {
  background-color: #34C759;
  color: white;
  border-color: #34C759;
}

.option-btn.wrong {
  background-color: #FF3B30;
  color: white;
  border-color: #FF3B30;
}

.feedback {
  margin-top: 10px;
  font-weight: bold;
  text-align: center;
}

.action-btn {
  width: 100%;
  padding: 12px;
  margin-top: 15px;
  background-color: #007AFF;
  color: white;
  border: none;
  border-radius: 8px;
  font-weight: bold;
  font-size: 1rem;
  cursor: pointer;
}

.score-box {
  text-align: center;
  font-size: 3rem;
  font-weight: bold;
  color: #34C759;
  margin: 15px 0;
}