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

body {
  background-color: #f0f2f5;
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 20px;
}

.app {
  background-color: white;
  width: 100%;
  max-width: 600px;
  border-radius: 16px;
  padding: 2rem;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
  transition: all 0.3s ease;
}

.app:hover {
  box-shadow: 0 15px 35px rgba(0, 0, 0, 0.15);
}

.app h1 {
  font-size: 28px;
  color: #2c3e50;
  font-weight: 700;
  padding-bottom: 20px;
  margin-bottom: 20px;
  border-bottom: 2px solid #ecf0f1;
  text-align: center;
}

.quiz {
  padding: 1rem 0;
}

.quiz h2 {
  font-size: 20px;
  color: #34495e;
  font-weight: 600;
  margin-bottom: 1.5rem;
  line-height: 1.4;
}

.btn {
  background-color: #f8f9fa;
  color: #2c3e50;
  font-weight: 500;
  width: 100%;
  border: 2px solid #dfe6e9;
  padding: 12px 20px;
  margin: 8px 0;
  text-align: left;
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.3s;
  font-size: 16px;
}

.btn:hover:not([disabled]) {
  background-color: #3498db;
  color: white;
  border-color: #3498db;
  transform: translateY(-2px);
}

.btn:disabled {
  cursor: not-allowed;
  opacity: 0.8;
}

#next-btn {
  background-color: #3498db;
  color: white;
  font-weight: 600;
  width: 150px;
  border: none;
  padding: 12px;
  margin: 25px auto 0;
  border-radius: 8px;
  cursor: pointer;
  display: none;
  font-size: 16px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  transition: all 0.3s;
}

#next-btn:hover {
  background-color: #2980b9;
  transform: translateY(-2px);
  box-shadow: 0 5px 15px rgba(41, 128, 185, 0.4);
}

.correct {
  background: #27ae60 !important;
  color: white !important;
  border-color: #27ae60 !important;
}

.incorrect {
  background: #e74c3c !important;
  color: white !important;
  border-color: #e74c3c !important;
}

/* Progress indicator */
.progress-container {
  width: 100%;
  height: 6px;
  background-color: #ecf0f1;
  border-radius: 3px;
  margin-bottom: 25px;
  overflow: hidden;
}

.progress-bar {
  height: 100%;
  background-color: #3498db;
  transition: width 0.4s ease;
}

/* Score display */
.score-display {
  text-align: center;
  font-size: 24px;
  color: #2c3e50;
  margin: 20px 0;
  font-weight: 700;
}

/* Loading state */
.loading {
  text-align: center;
  padding: 30px;
  color: #10373a;
  font-size: 18px;
}

.loading:after {
  content: '...';
  animation: dots 1.5s steps(5, end) infinite;
}

@keyframes dots {
  0%, 20% { content: '.'; }
  40% { content: '..'; }
  60%, 100% { content: '...'; }
}