body {
  background: #0a0a0a;
  color: #fff;
  font-family: 'Segoe UI', Arial, sans-serif;
  margin: 0;
  padding: 0;
}
main {
  max-width: 600px;
  margin: 2rem auto;
  padding: 2rem;
  background: #111;
  border-radius: 1rem;
  box-shadow: 0 4px 24px rgba(0,0,0,0.4);
}
h1 {
  text-align: center;
  font-weight: 300;
  letter-spacing: 2px;
  color: #ddd;
}
#countdown-display {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 1.5rem;
  margin: 3rem 0;
  min-height: 100px;
  perspective: 1000px;
}
.circle-container {
  position: relative;
  width: 64px;
  height: 64px;
}
.circle {
  width: 64px;
  height: 64px;
  border-radius: 50%;
  background: transparent;
  border: 3px solid rgba(255, 255, 255, 0.2);
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
  transform-style: preserve-3d;
  transition: background 0.3s, border 0.3s;
}
.circle.filled {
  background: rgba(255, 255, 255, 0.95);
  border-color: rgba(255, 255, 255, 1);
  box-shadow: 0 0 20px rgba(255, 255, 255, 0.4),
              0 0 40px rgba(255, 255, 255, 0.2);
}
.circle.flipping {
  animation: softFlip 0.6s cubic-bezier(0.4, 0.2, 0.2, 1);
  transition: none !important;
}

@keyframes softFlip {
  0% {
    transform: rotateX(0deg);
  }
  50% {
    transform: rotateX(90deg);
  }
  100% {
    transform: rotateX(0deg);
  }
}

#controls {
  display: flex;
  gap: 0.75rem;
  justify-content: center;
  flex-wrap: wrap;
}
input[type="number"] {
  width: 100px;
  padding: 0.75rem;
  border-radius: 0.5rem;
  border: 1px solid #444;
  background: #1a1a1a;
  color: #fff;
  font-size: 1rem;
}
button {
  padding: 0.75rem 1.5rem;
  border-radius: 0.5rem;
  border: 1px solid rgba(255, 255, 255, 0.3);
  background: rgba(255, 255, 255, 0.1);
  color: #fff;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.3s;
  letter-spacing: 1px;
}
button:hover {
  background: rgba(255, 255, 255, 0.2);
  border-color: rgba(255, 255, 255, 0.5);
  box-shadow: 0 0 15px rgba(255, 255, 255, 0.2);
}

@media (max-width: 600px) {
  .circle-container {
    width: 48px;
    height: 48px;
  }
  .circle {
    width: 48px;
    height: 48px;
    border: 2px solid rgba(255, 255, 255, 0.2);
  }
  #countdown-display {
    gap: 1rem;
  }
}