:root {
  --primary-color: #007bff;
  --primary-hover-color: #0056b3;
  --background-color: #f4f7f6;
  --container-bg-color: #ffffff;
  --text-color: #333;
  --border-color: #ddd;
  --success-color: #28a745;
  --error-color: #dc3545;
  --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
}

body {
  margin: 0;
  font-family: var(--font-family);
  background-color: var(--background-color);
  color: var(--text-color);
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  padding: 1rem;
  box-sizing: border-box;
}

h1, h2 {
  margin-top: 0;
  text-align: center;
  color: var(--text-color);
}

h1 {
  font-size: 1.75rem;
}

h2 {
  font-size: 1.5rem;
  margin-bottom: 1.5rem;
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 1rem;
}

p {
  color: #666;
  margin-bottom: 2rem;
  text-align: center;
}

.form-group {
  display: flex;
  flex-direction: column;
  text-align: left;
}

label {
  font-weight: 600;
  margin-bottom: 0.5rem;
}

input[type='text'],
input[type='password'] {
  width: 100%;
  padding: 0.75rem;
  border: 1px solid var(--border-color);
  border-radius: 8px;
  font-size: 1rem;
  box-sizing: border-box;
  transition: border-color 0.2s, box-shadow 0.2s;
}

input[type='text']:focus,
input[type='password']:focus {
  outline: none;
  border-color: var(--primary-color);
  box-shadow: 0 0 0 3px rgba(0, 123, 255, 0.2);
}

.submit-button {
  background-color: var(--primary-color);
  color: white;
  border: none;
  padding: 0.85rem;
  font-size: 1rem;
  font-weight: 600;
  border-radius: 8px;
  cursor: pointer;
  transition: background-color 0.2s, transform 0.1s;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 45px;
}
.submit-button:hover:not(:disabled) {
  background-color: var(--primary-hover-color);
  transform: translateY(-2px);
}
.submit-button:disabled {
  background-color: #a0c7ff;
  cursor: not-allowed;
}

.spinner {
  width: 20px;
  height: 20px;
  border: 3px solid rgba(255, 255, 255, 0.3);
  border-radius: 50%;
  border-top-color: #fff;
  animation: spin 1s ease-in-out infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

.action-button {
  background: none;
  border: 1px solid var(--border-color);
  color: var(--text-color);
  padding: 0.4rem 0.8rem;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.9rem;
  transition: background-color 0.2s, color 0.2s, border-color 0.2s;
}
.action-button:hover { background-color: #e9ecef; }