@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&family=JetBrains+Mono:wght@400;500&family=Noto+Sans+SC:wght@400;500;600;700&display=swap');

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-body);
  background: var(--bg-primary);
  color: var(--text-primary);
  min-height: 100vh;
  line-height: 1.6;
  overflow-x: hidden;
  transition: background-color 0.3s ease, color 0.3s ease;
}

a { color: var(--accent); text-decoration: none; }

::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border-primary); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--border-light); }

/* ===== App Layout ===== */
.app-layout {
  display: grid;
  grid-template-columns: var(--sidebar-width) 1fr;
  min-height: 100vh;
}

.app-layout.sidebar-collapsed {
  grid-template-columns: 0 1fr;
}

/* ===== Header ===== */
.header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 24px;
  height: var(--header-height);
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border-primary);
  backdrop-filter: blur(12px);
  position: sticky;
  top: 0;
  z-index: 100;
  grid-column: 1 / -1;
  transition: background-color 0.3s ease;
}

.header-logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--text-primary);
}

.header-logo .icon { font-size: 1.5rem; }

.header-actions {
  display: flex;
  align-items: center;
  gap: 12px;
}

.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  border: 1px solid var(--border-primary);
  background: var(--bg-card);
  color: var(--text-secondary);
  cursor: pointer;
  font-size: 1.2rem;
  transition: all var(--transition-fast);
}
.theme-toggle:hover {
  border-color: var(--accent);
  color: var(--accent);
  background: var(--accent-soft);
}

/* ===== Sidebar ===== */
.sidebar {
  position: sticky;
  background: var(--bg-sidebar);
  border-right: 1px solid var(--border-primary);
  overflow-y: auto;
  padding: 16px 0;
  top: var(--header-height);
  height: calc(100vh - var(--header-height));
  transition: transform 0.3s ease, width 0.3s ease, background-color 0.3s ease;
  z-index: 90;
}

.sidebar-section { padding: 0 12px; margin-bottom: 8px; }

.sidebar-section-title {
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
  padding: 10px 12px 6px;
}

.sidebar-item {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 14px;
  margin: 2px 0;
  border-radius: var(--radius-sm);
  font-size: 0.875rem;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition-fast);
  border-left: 3px solid transparent;
  user-select: none;
}
.sidebar-item:hover {
  background: var(--bg-sidebar-hover);
  color: var(--text-primary);
}
.sidebar-item.active {
  background: var(--bg-sidebar-active);
  border-left-color: var(--accent);
  color: var(--accent);
  font-weight: 600;
}
.sidebar-item .count {
  margin-left: auto;
  font-size: 0.7rem;
  color: var(--text-muted);
  background: var(--bg-tag);
  padding: 2px 8px;
  border-radius: 12px;
}

.sidebar-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  border: 1px solid var(--border-primary);
  background: var(--bg-card);
  color: var(--text-secondary);
  cursor: pointer;
  font-size: 0.85rem;
  transition: all var(--transition-fast);
}
.sidebar-toggle:hover {
  border-color: var(--accent);
  color: var(--accent);
  background: var(--accent-soft);
}

.sidebar.collapsed {
  width: 0;
  min-width: 0;
  padding: 0;
  border-right: none;
  overflow: hidden;
}
.sidebar.collapsed .sidebar-section-title,
.sidebar.collapsed .sidebar-item,
.sidebar.collapsed .tree-overview,
.sidebar.collapsed .tree-toggle,
.sidebar.collapsed .tree-lesson,
.sidebar.collapsed .tree-children { display: none; }

/* ===== Tree (Lesson sidebar) ===== */
.tree-item { position: relative; }

.tree-toggle {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 7px 14px;
  margin: 1px 0;
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition-fast);
  border-left: 3px solid transparent;
  user-select: none;
}
.tree-toggle:hover {
  background: var(--bg-sidebar-hover);
  color: var(--text-primary);
}
.tree-toggle.active {
  background: var(--bg-sidebar-active);
  border-left-color: var(--accent);
  color: var(--accent);
  font-weight: 600;
}
.tree-toggle .arrow {
  font-size: 0.6rem;
  transition: transform var(--transition-fast);
  width: 14px;
  text-align: center;
  flex-shrink: 0;
}
.tree-item.collapsed > .tree-toggle .arrow { transform: rotate(-90deg); }
.tree-item.collapsed > .tree-children { display: none; }

.tree-children { padding-left: 16px; }

.tree-overview {
  font-size: 0.88rem;
  font-weight: 600;
  padding: 8px 14px 8px 16px;
  margin: 2px 0 4px;
  border-left: 3px solid transparent;
  cursor: pointer;
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  transition: all var(--transition-fast);
  user-select: none;
}
.tree-overview:hover { background: var(--bg-sidebar-hover); }
.tree-overview.active {
  background: var(--bg-sidebar-active);
  border-left-color: var(--accent);
  color: var(--accent);
}

.tree-lesson {
  font-size: 0.82rem;
  padding: 6px 14px 6px 28px;
  border-left: 3px solid transparent;
  cursor: pointer;
  border-radius: var(--radius-sm);
  margin: 1px 0;
  color: var(--text-muted);
  transition: all var(--transition-fast);
}
.tree-lesson:hover { background: var(--bg-sidebar-hover); color: var(--text-primary); }
.tree-lesson.active {
  background: var(--bg-sidebar-active);
  border-left-color: var(--accent);
  color: var(--accent);
  font-weight: 600;
}

/* ===== Main Content ===== */
.main-content {
  padding: 24px 32px;
  min-height: calc(100vh - var(--header-height));
  animation: fadeIn 0.4s ease;
}

/* ===== Stats Bar ===== */
.stats-bar {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 16px;
  flex-wrap: wrap;
  padding: 10px 16px;
  margin-bottom: 24px;
  background: var(--bg-card);
  border: 1px solid var(--border-primary);
  border-radius: var(--radius-lg);
  font-size: 0.8rem;
  color: var(--text-muted);
  white-space: nowrap;
}
.stats-bar strong { color: var(--accent); }

/* ===== Search Area ===== */
.search-area {
  margin-bottom: 20px;
}

.search-wrapper {
  position: relative;
  max-width: 640px;
  margin: 0 auto;
}

.search-input {
  width: 100%;
  padding: 14px 48px 14px 20px;
  font-size: 1rem;
  font-family: var(--font-body);
  background: var(--bg-input);
  border: 2px solid var(--border-primary);
  border-radius: 50px;
  color: var(--text-primary);
  outline: none;
  transition: all var(--transition-normal);
}
.search-input:focus { border-color: var(--accent); box-shadow: 0 0 0 3px var(--accent-soft); }
.search-input::placeholder { color: var(--text-muted); }

.search-clear {
  position: absolute;
  right: 14px;
  top: 50%;
  transform: translateY(-50%);
  width: 28px;
  height: 28px;
  border-radius: 50%;
  border: none;
  background: var(--bg-tag);
  color: var(--text-muted);
  cursor: pointer;
  font-size: 0.9rem;
  display: none;
  align-items: center;
  justify-content: center;
  transition: all var(--transition-fast);
}
.search-clear:hover { background: var(--border-primary); color: var(--text-primary); }
.search-clear.visible { display: flex; }

.search-hint {
  text-align: center;
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-top: 8px;
}

/* ===== Category Tabs ===== */
.category-tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 20px;
  padding: 4px;
  background: var(--bg-card);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-primary);
}

.cat-tab {
  padding: 8px 20px;
  border-radius: 30px;
  font-size: 0.85rem;
  font-weight: 500;
  color: var(--text-secondary);
  cursor: pointer;
  border: none;
  background: transparent;
  transition: all var(--transition-fast);
  white-space: nowrap;
  font-family: var(--font-body);
}
.cat-tab:hover { color: var(--text-primary); background: var(--bg-tag-hover); }
.cat-tab.active {
  background: var(--accent);
  color: #fff;
  font-weight: 600;
}
.cat-tab .tab-count {
  margin-left: 4px;
  font-size: 0.7rem;
  opacity: 0.75;
}

/* ===== Molecule Grid ===== */
.molecule-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 12px;
  min-height: 200px;
}

.mol-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 20px 12px;
  background: var(--bg-card);
  border: 1px solid var(--border-primary);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all 0.2s ease;
  position: relative;
  overflow: hidden;
  animation: fadeInUp 0.35s ease both;
  gap: 8px;
}
.mol-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
  border-color: var(--accent-border);
}
.mol-card:active { transform: translateY(-1px); }

.mol-card .struct-icon {
  position: absolute;
  top: 8px;
  right: 8px;
  width: 28px;
  height: 28px;
  color: var(--accent);
  opacity: 0.4;
}
.mol-card:hover .struct-icon { opacity: 0.7; }

.mol-card .mol-formula {
  font-family: var(--font-chem);
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: 0.02em;
}

.mol-card .mol-name {
  font-size: 0.85rem;
  color: var(--text-secondary);
  font-weight: 500;
}

.mol-card .mol-eng {
  font-size: 0.7rem;
  color: var(--text-muted);
  font-style: italic;
  text-align: center;
  line-height: 1.2;
}

.mol-card .mol-struct-tag {
  font-size: 0.65rem;
  padding: 2px 8px;
  border-radius: 10px;
  background: var(--accent-soft);
  color: var(--accent);
}

/* ===== Empty State ===== */
.empty-state {
  grid-column: 1 / -1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 48px 24px;
  color: var(--text-muted);
}

.empty-state .empty-icon { font-size: 3rem; margin-bottom: 12px; opacity: 0.6; }
.empty-state .empty-text { font-size: 1rem; }
.empty-state .empty-hint { font-size: 0.8rem; margin-top: 4px; }

/* ===== Modal ===== */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: var(--bg-overlay);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 1000;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.2s ease, visibility 0.2s ease;
  backdrop-filter: blur(4px);
}
.modal-overlay.open { opacity: 1; visibility: visible; }

.modal-card {
  position: relative;
  background: var(--bg-modal);
  border: 1px solid var(--border-primary);
  border-radius: var(--radius-xl);
  padding: 32px 28px;
  max-width: 420px;
  width: 90%;
  box-shadow: var(--shadow-lg);
  transform: scale(0.95);
  transition: transform 0.2s ease;
  text-align: center;
}
.modal-overlay.open .modal-card { transform: scale(1); }

.modal-close {
  position: absolute;
  top: 12px;
  right: 12px;
  width: 36px;
  height: 36px;
  border-radius: 50%;
  border: 1px solid var(--border-primary);
  background: var(--bg-card);
  color: var(--text-secondary);
  cursor: pointer;
  font-size: 1.25rem;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition-fast);
}
.modal-close:hover { background: var(--border-primary); color: var(--text-primary); }

.modal-header {
  position: relative;
  margin-bottom: 20px;
}

.modal-formula {
  font-family: var(--font-chem);
  font-size: 2rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 4px;
}

.modal-name {
  font-size: 1.1rem;
  color: var(--accent);
  font-weight: 600;
}

.modal-eng {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-bottom: 6px;
  word-break: break-all;
}

.modal-struct {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  font-size: 0.75rem;
  color: var(--accent);
  background: var(--accent-soft);
  padding: 4px 12px;
  border-radius: 12px;
  margin-bottom: 16px;
}

.modal-links {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-bottom: 16px;
}

.modal-link {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 20px;
  border-radius: 40px;
  font-size: 0.9rem;
  font-weight: 600;
  color: #fff;
  text-decoration: none;
  transition: all var(--transition-fast);
  border: none;
  cursor: pointer;
}
.modal-link:hover { transform: translateY(-2px); box-shadow: var(--shadow-md); opacity: 0.9; }
.modal-link.molview { background: #276749; }
.modal-link.chemspider { background: #c05621; }
.modal-link.pubchem { background: #2b6cb0; }

.modal-hint {
  font-size: 0.7rem;
  color: var(--text-muted);
}

/* ===== Footer ===== */
.footer {
  text-align: center;
  padding: 20px 24px;
  font-size: 0.8rem;
  color: var(--text-muted);
  border-top: 1px solid var(--border-primary);
  grid-column: 2;
  transition: background-color 0.3s ease;
}

/* ===== Animations ===== */
@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}

/* ===== Responsive ===== */
@media (max-width: 1024px) {
  .molecule-grid { grid-template-columns: repeat(2, 1fr); }
}

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

  .footer { grid-column: 1; }

  .sidebar {
    position: fixed;
    top: var(--header-height);
    left: 0;
    bottom: 0;
    width: var(--sidebar-width);
    transform: translateX(0);
    box-shadow: var(--shadow-lg);
    z-index: 86;
  }
  .sidebar.collapsed {
    width: 0;
    min-width: 0;
    padding: 0;
    border-right: none;
    overflow: hidden;
    box-shadow: none;
    transform: translateX(0);
  }
  .sidebar.collapsed .sidebar-section-title,
  .sidebar.collapsed .sidebar-item,
  .sidebar.collapsed .tree-overview,
  .sidebar.collapsed .tree-toggle,
  .sidebar.collapsed .tree-lesson,
  .sidebar.collapsed .tree-children { display: none; }

  .app-layout.sidebar-collapsed { grid-template-columns: 1fr; }

  .main-content { padding: 16px; }

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

  .modal-card { width: 95%; padding: 24px 16px; }
}

@media (max-width: 480px) {
  .header { padding: 0 12px; }
  .header-logo { font-size: 0.95rem; gap: 6px; }
  .header-logo .icon { font-size: 1.2rem; }
  .cat-tab { padding: 6px 12px; font-size: 0.75rem; }
  .mol-card { padding: 14px 8px; }
  .mol-card .mol-formula { font-size: 1.2rem; }
}