body {
  background: radial-gradient(circle at top, #2d2d2d, #1a1a1a); /* 少し明るめのダーク背景 */
  color: white;
  font-family: system-ui, sans-serif;
}

.card {
  width: 100%;
  max-width: 420px;
  padding: 2.5rem;
  border-radius: 1.5rem;
  backdrop-filter: blur(16px);
  background: rgba(255,255,255,0.12); /* 背景を少し透明感のあるものに */
  border: 1px solid rgba(255,255,255,0.3);
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.5); /* カードに影をつけて立体感を増す */
  transition: 0.4s;
}

h1, label {
  text-align: center;
  font-size: 1.5rem;
  margin-bottom: 1rem;
  font-weight: bold;
}

input, button {
  width: 100%;
  padding: 1rem;
  border-radius: 0.75rem;
  margin-top: 1rem;
  font-size: 1rem; /* フォントサイズを少し大きく */
}

input {
  background: rgba(255, 255, 255, 0.15);
  border: 1px solid rgba(255, 255, 255, 0.3);
  color: white;
}

button {
  background: linear-gradient(90deg, #4f46e5, #2563eb);
  border: none;
  color: white;
  font-weight: bold;
  cursor: pointer;
  transition: background 0.3s ease;
}

button:hover {
  background: linear-gradient(90deg, #4f46e5, #9333ea); /* ボタンにホバー時の色変化 */
}

.error {
  color: #f87171;
  text-align: center;
  margin-top: 1rem;
  font-size: 1rem;
}

.hidden {
  display: none;
}

.guest {
  display: block;
  width: 100%;
  margin-top: 1.5rem;
  padding: 0.75rem;
  border-radius: 0.75rem;
  background-color: #4b5563;
  color: white;
  font-weight: bold;
  text-align: center;
  transition: background-color 0.3s;
}

.guest:hover {
  background-color: #6b7280;
}

#loadingSpinner {
  display: flex;
  justify-content: center;
  align-items: center;
  margin-top: 1rem;
  font-size: 2rem;
}

#flash {
  position: fixed;
  inset: 0;
  background: #fff;
  opacity: 0;
  pointer-events: none;
  z-index: 50;
}