* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html,
body {
  min-height: 100%;
  font-family: sans-serif;
  background: #f4f4f4;
  color: #333;
}

/* Landing Page */
#landing {
  min-height: 90vh;
  padding: 0.75rem;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background: #f4f4f4;
  text-align: center;
  transition: opacity 0.6s ease;
  z-index: 10;
  animation: fadeIn 1s ease-in-out;
}

#landing.hidden {
  opacity: 0;
  pointer-events: none;
  position: absolute;
}

#coverImage {
  max-width: 240px;
  width: 100%;
  height: auto;
  margin-bottom: 0.75rem;
  border-radius: 6px;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

#coverImage:hover {
  transform: scale(1.02);
  box-shadow: 0 6px 18px rgba(0, 0, 0, 0.25);
}

#landing h1 {
  font-size: 1.75rem;
  margin: 0.5rem 0 1rem;
  color: #222;
  max-width: 90%;
}

/* Start Button Wrapper */
#btnStartWrapper {
  display: inline-block;
  width: 220px;
  height: 64px;
  border-radius: 6px;
  overflow: hidden;
  cursor: pointer;
  transition: transform 0.2s ease;
}

#btnStartWrapper:hover {
  transform: scale(1.03);
}

#btnStart {
  width: 100%;
  height: 100%;
  object-fit: cover;
  display: block;
  border: none;
  color: #fff;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.2s ease, background 0.3s ease;
}

/* Flipbook Container */
#df_manual_book {
  display: none;
  width: 100%;
  height: 100vh;
}

/* Spinner */
#spinner {
  position: fixed;
  inset: 0;
  display: none;
  justify-content: center;
  align-items: center;
  background: rgba(255, 255, 255, 0.8);
  z-index: 20;
}

.spinner-icon {
  border: 5px solid #f3f3f3;
  border-top: 5px solid #007bff;
  border-radius: 50%;
  width: 50px;
  height: 50px;
  animation: spin 1s linear infinite;
}

/* Animations */
@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* Responsive */
@media (max-width: 768px) {
  #landing h1 {
    font-size: 1.5rem;
  }

  #coverImage {
    max-width: 200px;
  }
}

@media (max-width: 480px) {
  #landing h1 {
    font-size: 1.25rem;
  }

  #coverImage {
    max-width: 180px;
  }

  .spinner-icon {
    width: 40px;
    height: 40px;
    border-width: 4px;
  }
}