body {
  margin: 0;
  font-family: 'Segoe UI', Roboto, Arial, sans-serif;
  background: #0b0d12;
  color: #e6e9ef;
  display: flex;
  flex-direction: column;
  align-items: center;
  min-height: 100vh;
}

header {
  text-align: center;
  margin: 30px 0 10px;
}

h1 {
  color: #66b2ff;
  margin-bottom: 5px;
}

#controls {
  display: flex;
  gap: 10px;
  justify-content: center;
  margin-bottom: 20px;
}

select, button {
  background: #11161c;
  color: #e6e9ef;
  border: 1px solid #3a6fa5;
  border-radius: 6px;
  padding: 6px 10px;
  cursor: pointer;
  font-size: 14px;
}

button:hover, select:hover {
  background: #1b2530;
}

#cardContainer {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 20px;
  max-width: 1200px;
}

.card {
  background: #101820;
  border: 1px solid #3a6fa5;
  border-radius: 12px;
  width: 250px;
  height: 150px;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  font-size: 16px;
  color: #d8e4f7;
  box-shadow: 0 0 10px #0077ff44;
  transition: transform 0.6s;
  transform-style: preserve-3d;
  cursor: pointer;
  position: relative;
}

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

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

.card-face {
  position: absolute;
  width: 100%;
  height: 100%;
  backface-visibility: hidden;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 10px;
  border-radius: 12px;
}

.front {
  background: #101820;
}

.back {
  background: #13202d;
  color: #a4ffb6;
  transform: rotateY(180deg);
}

footer {
  margin-top: auto;
  text-align: center;
  color: #999;
  font-size: 13px;
  padding: 20px;
}