/* Tablet: 768px - 1024px */
@media (max-width: 1024px) {
  .app {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: fixed;
    top: 0;
    left: 0;
    width: var(--sidebar-width);
    height: 100vh;
    z-index: 100;
    transform: translateX(-100%);
    transition: transform var(--transition-normal);
    padding-top: var(--space-6);
  }

  .sidebar.open {
    transform: translateX(0);
  }

  .toc {
    display: none;
  }

  .main {
    grid-column: 1;
    padding: var(--space-6) var(--space-6);
  }

  .menu-btn {
    display: flex;
  }

  .header__nav {
    display: none;
  }

  .search {
    max-width: 300px;
  }

  .home__subjects {
    grid-template-columns: repeat(2, 1fr);
  }

  /* Floating TOC button */
  .toc-fab {
    display: flex;
  }
}

/* Mobile: < 768px */
@media (max-width: 768px) {
  :root {
    --header-height: 52px;
  }

  .header {
    padding: 0 var(--space-4);
    gap: var(--space-2);
  }

  .header__logo span {
    display: none;
  }

  .search {
    max-width: 200px;
  }

  .search__kbd {
    display: none;
  }

  .sidebar {
    width: 85%;
    max-width: 320px;
  }

  .main {
    padding: var(--space-4) var(--space-4);
  }

  .article h1 {
    font-size: var(--text-2xl);
  }

  .article h2 {
    font-size: var(--text-xl);
  }

  .article h3 {
    font-size: var(--text-lg);
  }

  .article pre {
    margin-left: calc(-1 * var(--space-4));
    margin-right: calc(-1 * var(--space-4));
    border-radius: 0;
    padding: var(--space-4);
  }

  .article table {
    display: block;
    overflow-x: auto;
  }

  .home {
    padding: var(--space-8) var(--space-4);
  }

  .home__title {
    font-size: var(--text-2xl);
  }

  .home__subtitle {
    font-size: var(--text-base);
  }

  .home__subjects {
    grid-template-columns: 1fr;
  }

  .search-results {
    width: 95%;
    max-height: 60vh;
  }

  .review-grid {
    grid-template-columns: 1fr;
  }

  .breadcrumb {
    font-size: var(--text-xs);
  }
}

/* Small mobile: < 480px */
@media (max-width: 480px) {
  .header__right {
    gap: var(--space-1);
  }

  .search {
    max-width: 160px;
  }

  .article h1 {
    font-size: var(--text-xl);
  }

  .key-point, .high-freq-box {
    padding: var(--space-3);
    margin-left: calc(-1 * var(--space-4));
    margin-right: calc(-1 * var(--space-4));
    border-radius: 0;
  }
}

/* Floating TOC button (tablet/mobile) */
.toc-fab {
  display: none;
  position: fixed;
  bottom: var(--space-6);
  right: var(--space-6);
  width: 48px;
  height: 48px;
  align-items: center;
  justify-content: center;
  background: var(--color-primary);
  color: var(--color-bg);
  border-radius: 50%;
  box-shadow: 0 4px 12px var(--color-shadow);
  z-index: 50;
  transition: transform var(--transition-fast);
}

.toc-fab:hover {
  transform: scale(1.1);
}

.toc-fab svg {
  width: 20px;
  height: 20px;
}

/* TOC bottom sheet (mobile) */
.toc-sheet {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  max-height: 60vh;
  background: var(--color-bg);
  border-top: 1px solid var(--color-border);
  border-radius: var(--radius-lg) var(--radius-lg) 0 0;
  box-shadow: 0 -4px 20px var(--color-shadow);
  z-index: 150;
  padding: var(--space-4) var(--space-6);
  overflow-y: auto;
  transform: translateY(100%);
  transition: transform var(--transition-normal);
}

.toc-sheet.open {
  transform: translateY(0);
}

.toc-sheet__handle {
  width: 36px;
  height: 4px;
  background: var(--color-gray-300);
  border-radius: var(--radius-full);
  margin: 0 auto var(--space-4);
}

.toc-sheet__title {
  font-size: var(--text-sm);
  font-weight: 600;
  margin-bottom: var(--space-3);
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* Prefers reduced motion */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}