body {
  margin: 0;
  font-family: Arial, sans-serif;
  background: #f5f5f5;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  color: #333;
}

.container {
  text-align: center;
}

h1 {
  margin-bottom: 20px;
  font-weight: 600;
}

.card {
  width: 300px;
  height: 180px;
  perspective: 1000px;
  margin: 0 auto 15px;
  cursor: pointer;
}

.card-inner {
  width: 100%;
  height: 100%;
  position: relative;
  transition: transform 0.6s;
  transform-style: preserve-3d;
}

.card.flipped .card-inner {
  transform: rotateY(180deg);
}

.card-front, .card-back {
  position: absolute;
  width: 100%;
  height: 100%;
  backface-visibility: hidden;
  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 22px;
  background: white;
  border-radius: 12px;
  box-shadow: 0 4px 12px rgba(0,0,0,0.1);
}

.card-back {
  transform: rotateY(180deg);
}

.buttons {
  margin-top: 15px;
}

button {
  padding: 10px 14px;
  margin: 5px;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  background: #333;
  color: white;
  font-size: 14px;
}

button:hover {
  background: #555;
}

.progress {
  margin-top: 10px;
  font-size: 14px;
  color: #666;
}


.level-selector {
  margin-bottom: 15px;
}

select {
  padding: 6px 10px;
  border-radius: 6px;
  border: 1px solid #ccc;
  background: white;
}