/* ===== RESET & BASE ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; font-size: 16px; -webkit-font-smoothing: antialiased; -moz-osx-font-smoothing: grayscale; }

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  overflow-x: hidden;
}

/* Accessibility: skip link */
.skip-link {
  position: absolute; left: -9999px; top: auto;
  background: var(--accent-primary); color: #fff; padding: 8px 16px;
  z-index: 10000; border-radius: 8px; font-weight: 600;
}
.skip-link:focus { left: 16px; top: 16px; }

/* ===== TYPOGRAPHY ===== */
h1 { font-size: 2.25rem; font-weight: 800; letter-spacing: -0.025em; line-height: 1.2; }
h2 { font-size: 1.75rem; font-weight: 700; letter-spacing: -0.02em; }
h3 { font-size: 1.2rem; font-weight: 650; letter-spacing: -0.01em; }
h4 { font-size: 1rem; font-weight: 600; }
a { color: var(--accent-primary); text-decoration: none; }
a:hover { text-decoration: underline; }

.section-title {
  text-align: center; margin: 3rem 0 1.75rem;
  color: var(--text-primary); font-size: 1.6rem;
}

/* ===== CONTAINER ===== */
.container { max-width: 1240px; margin: 0 auto; padding: 0 1.5rem 2.5rem; }

/* ===== NAVBAR ===== */
.navbar {
  position: sticky; top: 0; z-index: 1000;
  background: var(--navbar-bg);
  backdrop-filter: blur(20px) saturate(180%); -webkit-backdrop-filter: blur(20px) saturate(180%);
  border-bottom: 1px solid var(--border-color);
}
.navbar-inner {
  max-width: 1240px; margin: 0 auto;
  display: flex; align-items: center; justify-content: space-between;
  padding: 0 1.5rem; height: 64px; gap: 1.25rem;
}
.logo {
  display: flex; align-items: center; gap: 0.6rem;
  font-weight: 800; font-size: 1.2rem; color: var(--text-primary);
  text-decoration: none; letter-spacing: -0.02em;
}
.logo-icon { font-size: 1.4rem; }

.nav-links { display: flex; gap: 0.2rem; flex-wrap: nowrap; }
.nav-link {
  padding: 0.45rem 0.65rem; border-radius: 10px; font-weight: 550;
  color: var(--text-secondary); font-size: 0.82rem; text-decoration: none; white-space: nowrap;
  transition: background 0.2s, color 0.2s, box-shadow 0.2s;
}
.nav-link:hover, .nav-link:focus {
  background: var(--accent-subtle); color: var(--accent-primary); text-decoration: none;
}
.nav-link.active {
  background: var(--accent-primary); color: #fff;
  box-shadow: 0 2px 8px var(--accent-glow);
}

.nav-actions { display: flex; align-items: center; gap: 0.6rem; }

/* Search */
.search-wrapper { position: relative; }
#global-search {
  background: var(--bg-tertiary); border: 1px solid var(--border-color);
  border-radius: 10px; padding: 0.45rem 0.85rem 0.45rem 2.2rem;
  font-size: 0.85rem; color: var(--text-primary); width: 200px; outline: none;
  transition: border-color 0.2s, width 0.3s, box-shadow 0.2s;
  font-family: inherit;
}
#global-search:focus {
  border-color: var(--accent-primary); width: 260px;
  box-shadow: 0 0 0 3px var(--ring-2);
}
.search-wrapper::before {
  content: '\1F50D'; position: absolute; left: 10px; top: 50%; transform: translateY(-50%);
  font-size: 0.8rem; pointer-events: none; opacity: 0.5;
}
.search-dropdown {
  position: absolute; top: calc(100% + 6px); left: 0; right: 0;
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 12px; max-height: 300px; overflow-y: auto;
  box-shadow: var(--shadow-xl); z-index: 999;
}
.search-dropdown .search-item {
  padding: 0.6rem 0.85rem; cursor: pointer; font-size: 0.85rem;
  display: flex; align-items: center; gap: 0.6rem;
  border-bottom: 1px solid var(--border-color);
  transition: background 0.15s;
}
.search-dropdown .search-item:last-child { border-bottom: none; }
.search-dropdown .search-item:hover, .search-dropdown .search-item:focus,
.search-dropdown .search-item--focused {
  background: var(--accent-subtle);
}
.search-item .badge {
  font-size: 0.65rem; padding: 2px 8px; border-radius: 6px; font-weight: 700;
  text-transform: uppercase; letter-spacing: 0.04em;
}
.badge-physics { background: var(--accent-physics); color: #fff; }
.badge-biology { background: var(--accent-biology); color: #fff; }
.badge-chemistry { background: var(--accent-chemistry); color: #fff; }
.badge-mathematics { background: var(--accent-mathematics); color: #fff; }

/* Icon buttons */
.icon-btn {
  background: var(--bg-tertiary); border: 1px solid var(--border-color);
  width: 38px; height: 38px; border-radius: 10px; cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  font-size: 1.05rem; transition: all 0.2s;
  color: var(--text-primary);
}
.icon-btn:hover { background: var(--border-color); border-color: var(--border-hover); }

/* Hamburger */
.mobile-only { display: none; }
.hamburger {
  width: 18px; height: 2px; background: var(--text-primary);
  position: relative; border-radius: 2px;
}
.hamburger::before, .hamburger::after {
  content: ''; position: absolute; left: 0; width: 18px; height: 2px;
  background: var(--text-primary); border-radius: 2px;
}
.hamburger::before { top: -6px; }
.hamburger::after { top: 6px; }

/* Mobile Slide-out Drawer */
.mobile-drawer-overlay {
  position: fixed; inset: 0; z-index: 2000;
  background: rgba(0, 0, 0, 0.45);
  backdrop-filter: blur(8px); -webkit-backdrop-filter: blur(8px);
  opacity: 0; pointer-events: none;
  transition: opacity 0.25s cubic-bezier(0.16, 1, 0.3, 1);
  display: flex; justify-content: flex-end;
}
.mobile-drawer-overlay.open {
  opacity: 1; pointer-events: auto;
}
.mobile-drawer {
  width: min(320px, 86vw); height: 100%;
  background: var(--bg-card);
  border-left: 1px solid var(--border-color);
  box-shadow: -8px 0 32px rgba(0, 0, 0, 0.25);
  display: flex; flex-direction: column;
  transform: translateX(100%);
  transition: transform 0.28s cubic-bezier(0.16, 1, 0.3, 1);
  padding: env(safe-area-inset-top, 1rem) 0 env(safe-area-inset-bottom, 1rem);
}
.mobile-drawer-overlay.open .mobile-drawer {
  transform: translateX(0);
}
.mobile-drawer-header {
  display: flex; align-items: center; justify-content: space-between;
  padding: 1rem 1.25rem 0.85rem;
  border-bottom: 1px solid var(--border-color);
}
.close-drawer-btn {
  font-size: 1.4rem; line-height: 1;
}
.mobile-drawer-nav {
  display: flex; flex-direction: column; gap: 0.35rem;
  padding: 1rem 0.85rem; overflow-y: auto; flex: 1;
}
.mobile-nav-link {
  display: flex; align-items: center; gap: 0.85rem;
  padding: 0.75rem 1rem; border-radius: 12px;
  font-size: 1rem; font-weight: 600;
  color: var(--text-primary); text-decoration: none;
  transition: background 0.15s, color 0.15s;
}
.mobile-nav-link:hover {
  background: var(--accent-subtle); color: var(--accent-primary);
}
.mobile-nav-link.active {
  background: var(--accent-primary); color: #fff;
}
.mobile-nav-link .nav-ico {
  font-size: 1.2rem; width: 24px; text-align: center;
}
.mobile-drawer-footer {
  padding: 1rem 1.25rem;
  border-top: 1px solid var(--border-color);
  background: var(--bg-secondary);
}
.drawer-actions {
  display: flex; flex-direction: column; gap: 0.5rem;
}
.drawer-action-btn {
  display: flex; align-items: center; gap: 0.75rem;
  padding: 0.65rem 0.85rem; border-radius: 10px;
  background: var(--bg-card); border: 1px solid var(--border-color);
  color: var(--text-primary); font-size: 0.9rem; font-weight: 550;
  cursor: pointer; width: 100%; transition: background 0.15s;
}
.drawer-action-btn:hover {
  background: var(--accent-subtle);
}

/* Mobile Collapsible Search Bar */
.mobile-search-bar {
  position: sticky; top: 64px; z-index: 998;
  background: var(--bg-card);
  border-bottom: 1px solid var(--border-color);
  padding: 0.65rem 1rem;
  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.08);
}
.mobile-search-inner {
  display: flex; align-items: center; gap: 0.5rem;
  background: var(--input-bg);
  border: 1.5px solid var(--border-color);
  border-radius: 12px; padding: 0.4rem 0.75rem;
}
.mobile-search-inner:focus-within {
  border-color: var(--accent-primary);
  box-shadow: 0 0 0 3px var(--ring-2);
}
.mobile-search-inner input {
  flex: 1; border: none; background: transparent;
  color: var(--text-primary); font-size: 16px; outline: none;
  font-family: inherit;
}
.mobile-search-close-btn {
  background: none; border: none; font-size: 1.25rem;
  color: var(--text-muted); cursor: pointer; padding: 0 4px;
}
.mobile-search-dropdown {
  position: absolute; top: calc(100% + 4px); left: 1rem; right: 1rem;
  max-height: 50vh; overflow-y: auto;
}

/* ===== HERO ===== */
.hero {
  position: relative; overflow: hidden;
  background: var(--hero-gradient);
  padding: 5.5rem 1.5rem 4.5rem; text-align: center; color: #fff;
}
.hero-content { position: relative; z-index: 2; max-width: 720px; margin: 0 auto; }
.hero h1 { font-size: 3.2rem; line-height: 1.1; margin-bottom: 1.25rem; color: #fff; letter-spacing: -0.03em; }
.hero .highlight {
  background: linear-gradient(90deg, #fbbf24, #f97316, #ef4444);
  -webkit-background-clip: text; -webkit-text-fill-color: transparent;
  background-clip: text;
}
.hero-sub { font-size: 1.15rem; opacity: 0.9; margin-bottom: 2.25rem; line-height: 1.7; }
.hero-actions { display: flex; gap: 1rem; justify-content: center; flex-wrap: wrap; }

/* Floating shapes */
.hero-bg-shapes { position: absolute; inset: 0; pointer-events: none; overflow: hidden; }
.shape {
  position: absolute; border-radius: 50%; opacity: 0.1;
  animation: float 10s ease-in-out infinite;
  filter: blur(1px);
}
.shape-1 { width: 350px; height: 350px; background: #fbbf24; top: -80px; left: -100px; }
.shape-2 { width: 250px; height: 250px; background: #f97316; bottom: -60px; right: 8%; animation-delay: 3s; }
.shape-3 { width: 180px; height: 180px; background: #22c55e; top: 15%; right: -50px; animation-delay: 5s; }
@keyframes float {
  0%, 100% { transform: translateY(0) rotate(0deg) scale(1); }
  50% { transform: translateY(-25px) rotate(6deg) scale(1.03); }
}

/* ===== BUTTONS ===== */
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 0.4rem;
  padding: 0.6rem 1.35rem; border-radius: 10px; font-weight: 600;
  font-size: 0.875rem; border: 1.5px solid transparent; cursor: pointer;
  transition: all 0.2s ease; text-decoration: none; white-space: nowrap;
  font-family: inherit; letter-spacing: -0.01em;
}
.btn:focus-visible { outline: 2px solid var(--accent-primary); outline-offset: 2px; }
.btn:active { transform: scale(0.97); }

.btn-primary {
  background: var(--accent-primary); color: #fff; border-color: var(--accent-primary);
  box-shadow: 0 2px 8px var(--accent-glow);
}
.btn-primary:hover { background: var(--accent-hover); border-color: var(--accent-hover); box-shadow: 0 4px 16px var(--accent-glow); }
.btn-outline { background: transparent; color: var(--accent-primary); border-color: var(--accent-primary); }
.btn-outline:hover { background: var(--accent-primary); color: #fff; box-shadow: 0 2px 8px var(--accent-glow); }
.btn-ghost { background: transparent; color: var(--text-secondary); border-color: var(--border-color); }
.btn-ghost:hover { background: var(--bg-tertiary); color: var(--text-primary); border-color: var(--border-hover); }
.btn-lg { padding: 0.85rem 2.25rem; font-size: 1rem; border-radius: 12px; }
.btn-sm { padding: 0.35rem 0.85rem; font-size: 0.8rem; }
.btn-row { display: flex; gap: 0.5rem; flex-wrap: wrap; margin: 0.85rem 0; }
.btn-bookmark { transition: all 0.2s; }
.btn-bookmark.bookmarked { color: var(--warning); border-color: var(--warning); background: var(--warning-soft); }

/* ===== SUBJECT CARDS ===== */
.subject-grid {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 1.5rem; margin-bottom: 2.5rem;
}
.subject-card {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 20px; padding: 2rem 2rem 2.25rem; cursor: pointer;
  position: relative; overflow: hidden;
  transition: transform 0.3s cubic-bezier(.22,.68,0,1.2), box-shadow 0.3s, border-color 0.3s;
}
.subject-card:hover, .subject-card:focus {
  transform: translateY(-6px); box-shadow: var(--shadow-lg);
}
.physics-card:hover { border-color: var(--accent-physics); box-shadow: 0 12px 40px rgba(79,110,247,0.15); }
.biology-card:hover { border-color: var(--accent-biology); box-shadow: 0 12px 40px rgba(34,197,94,0.15); }
.chemistry-card:hover { border-color: var(--accent-chemistry); box-shadow: 0 12px 40px rgba(249,115,22,0.15); }
.mathematics-card:hover { border-color: var(--accent-mathematics); box-shadow: 0 12px 40px rgba(224,64,251,0.15); }
.card-icon { font-size: 2.75rem; margin-bottom: 0.85rem; }
.subject-card h3 { margin-bottom: 0.5rem; font-size: 1.3rem; }
.subject-card p { color: var(--text-secondary); font-size: 0.9rem; line-height: 1.55; }
.card-arrow {
  position: absolute; bottom: 1.5rem; right: 1.5rem;
  font-size: 1.35rem; color: var(--text-muted);
  transition: transform 0.3s, color 0.3s;
}
.subject-card:hover .card-arrow { transform: translateX(5px); color: var(--accent-primary); }

/* ===== STATS BAR ===== */
.stats-bar {
  display: flex; gap: 1.5rem; justify-content: center; flex-wrap: wrap;
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 16px; padding: 1.5rem 2.5rem;
  box-shadow: var(--shadow-xs);
}
.stat { text-align: center; min-width: 90px; }
.stat strong { display: block; font-size: 1.75rem; color: var(--accent-primary); font-weight: 800; letter-spacing: -0.02em; }
.stat span { font-size: 0.8rem; color: var(--text-muted); font-weight: 500; }

/* ===== PAGE HEADERS ===== */
.page-header {
  padding: 3rem 1.5rem 1.75rem; text-align: center;
}
.page-header h1 { margin-bottom: 0.5rem; font-size: 2rem; }
.page-header p { color: var(--text-secondary); font-size: 1rem; }
.physics-header h1 { color: var(--accent-physics); }
.biology-header h1 { color: var(--accent-biology); }
.chemistry-header h1 { color: var(--accent-chemistry); }
.mathematics-header h1 { color: var(--accent-mathematics); }

/* ===== TABS ===== */
.module-tabs {
  display: flex; gap: 0.3rem; flex-wrap: wrap;
  background: var(--bg-tertiary); border-radius: 14px; padding: 5px;
  margin-bottom: 1.75rem; border: 1px solid var(--border-color);
}
.tab {
  padding: 0.55rem 1.15rem; border-radius: 10px; border: none;
  background: transparent; color: var(--text-muted); cursor: pointer;
  font-weight: 600; font-size: 0.85rem; transition: all 0.2s;
  font-family: inherit; white-space: nowrap;
}
.tab:hover { color: var(--text-primary); background: var(--ring-2); }
.tab.active {
  background: var(--bg-card); color: var(--accent-primary);
  box-shadow: var(--shadow-sm); border: 1px solid var(--border-color);
}
.tab .tab-check {
  display: none;
  font-size: 0.7rem;
  margin-left: 0.3rem;
  color: var(--success);
}
.tab .tab-check.visible {
  display: inline;
}
.tab-panel { animation: fadeIn 0.3s ease; }
.tab-panel[hidden] { display: none; }
@keyframes fadeIn { from { opacity: 0; transform: translateY(8px); } to { opacity: 1; transform: translateY(0); } }

/* ===== SIMULATION LAYOUTS ===== */
.sim-layout {
  display: grid; grid-template-columns: 1fr 330px; gap: 1.5rem;
  align-items: start;
}
.sim-canvas-wrap {
  position: relative; background: var(--canvas-bg);
  border: 1px solid var(--border-color); border-radius: 16px; overflow: hidden;
  box-shadow: var(--shadow-sm);
}
.sim-canvas-wrap canvas { display: block; width: 100%; height: auto; }

.sim-controls {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 16px; padding: 1.5rem;
  box-shadow: var(--shadow-xs);
}
.sim-controls h3 { margin-bottom: 0.85rem; font-size: 1.1rem; }
.sim-controls label {
  display: block; font-size: 0.85rem; color: var(--text-secondary);
  margin-bottom: 0.7rem; font-weight: 500;
}
.sim-controls label span { font-weight: 700; color: var(--text-primary); }
.sim-controls input[type="range"] {
  width: 100%; margin-top: 0.3rem; accent-color: var(--accent-primary);
  height: 6px; border-radius: 3px;
}
.sim-controls input[type="text"],
.sim-controls input[type="search"],
.sim-controls select {
  width: 100%; padding: 0.5rem 0.75rem; border-radius: 10px;
  border: 1px solid var(--border-color); background: var(--input-bg);
  color: var(--text-primary); font-size: 0.875rem; font-family: inherit;
  margin-top: 0.25rem; transition: border-color 0.2s, box-shadow 0.2s;
}
.sim-controls input[type="text"]:focus,
.sim-controls input[type="search"]:focus,
.sim-controls select:focus {
  border-color: var(--accent-primary); outline: none;
  box-shadow: 0 0 0 3px var(--ring-2);
}

/* Experiment description box */
.experiment-info {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 16px; padding: 1.5rem 1.75rem; margin-bottom: 1.5rem;
  line-height: 1.7; box-shadow: var(--shadow-xs);
  border-left: 4px solid var(--accent-primary);
  cursor: pointer;
  user-select: none;
}
.experiment-info h3 {
  margin-bottom: 0.6rem; font-size: 1.15rem; color: var(--text-primary);
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.experiment-info h3::after {
  content: '\25BC';
  font-size: 0.7rem;
  color: var(--text-muted);
  transition: transform 0.3s;
  flex-shrink: 0;
  margin-left: 0.5rem;
}
.experiment-info.collapsed h3::after {
  transform: rotate(-90deg);
}
.experiment-info .info-body {
  overflow: hidden;
  max-height: 500px;
  transition: max-height 0.3s ease, opacity 0.3s ease, margin-top 0.3s ease;
  opacity: 1;
  margin-top: 0.5rem;
}
.experiment-info.collapsed .info-body {
  max-height: 0;
  opacity: 0;
  margin-top: 0;
}
.experiment-info.collapsed h3 {
  margin-bottom: 0;
}
.experiment-info p {
  font-size: 0.9rem; color: var(--text-secondary); margin-bottom: 0.5rem;
}
.experiment-info p:last-child { margin-bottom: 0; }
.experiment-info .key-concepts {
  display: flex; flex-wrap: wrap; gap: 0.4rem; margin-top: 0.75rem;
}
.experiment-info .concept-tag {
  background: var(--accent-subtle); color: var(--accent-primary);
  font-size: 0.75rem; padding: 0.25rem 0.7rem; border-radius: 20px;
  font-weight: 600; border: 1px solid var(--ring-1);
}
.experiment-info .real-world {
  margin-top: 0.75rem; padding-top: 0.75rem; border-top: 1px solid var(--border-color);
  font-size: 0.85rem; color: var(--text-muted); font-style: italic;
}

/* Formula / info boxes */
.formula-box, .info-box {
  background: var(--bg-tertiary); border-radius: 12px; padding: 1rem;
  margin-top: 0.85rem; font-size: 0.85rem;
  border: 1px solid var(--border-color);
}
.formula-box h4, .info-box h4 { margin-bottom: 0.4rem; }
.formula-box p { font-family: 'Courier New', monospace; margin: 0.2rem 0; color: var(--text-secondary); }
.results-panel { margin-top: 0.5rem; padding-top: 0.5rem; border-top: 1px solid var(--border-color); font-size: 0.8rem; color: var(--text-secondary); }

/* Legend */
.legend { display: flex; gap: 1rem; flex-wrap: wrap; margin-top: 0.6rem; font-size: 0.8rem; }
.legend-item { display: flex; align-items: center; gap: 0.35rem; }
.dot { width: 10px; height: 10px; border-radius: 50%; display: inline-block; }

/* Energy bar */
.energy-bar-container { margin-top: 1rem; }
.energy-bar {
  display: flex; height: 26px; border-radius: 13px; overflow: hidden;
  background: var(--bg-tertiary); border: 1px solid var(--border-color);
}
.energy-ke { background: linear-gradient(90deg, #ff7043, #ff5722); transition: width 0.1s; }
.energy-pe { background: linear-gradient(90deg, #42a5f5, #1e88e5); transition: width 0.1s; }

/* ===== CELL EXPLORER ===== */
.cell-controls-row {
  display: flex; gap: 0.75rem; align-items: center; margin-bottom: 1.25rem; flex-wrap: wrap;
}
.zoom-label { font-size: 0.85rem; display: flex; align-items: center; gap: 0.5rem; color: var(--text-secondary); font-weight: 500; }
.zoom-label input { width: 120px; }
.cell-layout { display: grid; grid-template-columns: 1fr 300px; gap: 1.5rem; }
.cell-canvas-wrap {
  background: var(--canvas-bg); border: 1px solid var(--border-color);
  border-radius: 16px; overflow: hidden; box-shadow: var(--shadow-sm);
}
.cell-canvas-wrap canvas { display: block; width: 100%; height: auto; cursor: pointer; }
.cell-info-panel {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 16px; padding: 1.5rem; box-shadow: var(--shadow-xs);
}
.cell-info-panel h3 { margin-bottom: 0.6rem; }
#cell-detail h4 { color: var(--accent-biology); margin: 0.6rem 0 0.3rem; }
#cell-detail p { font-size: 0.85rem; color: var(--text-secondary); line-height: 1.55; }

/* ===== DNA ===== */
.dna-layout { display: grid; grid-template-columns: 1fr 330px; gap: 1.5rem; }
.dna-canvas-wrap {
  background: var(--canvas-bg); border: 1px solid var(--border-color);
  border-radius: 16px; overflow: hidden; box-shadow: var(--shadow-sm);
}
.dna-canvas-wrap canvas { display: block; width: 100%; height: auto; }
.dna-controls {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 16px; padding: 1.5rem; box-shadow: var(--shadow-xs);
}
.dna-controls h3 { margin-bottom: 0.85rem; }
.dna-controls label { display: block; font-size: 0.85rem; color: var(--text-secondary); margin-bottom: 0.5rem; font-weight: 500; }
.dna-controls input[type="text"] {
  width: 100%; padding: 0.5rem 0.75rem; border-radius: 10px;
  border: 1px solid var(--border-color); background: var(--input-bg);
  color: var(--text-primary); font-family: 'Courier New', monospace; font-size: 0.9rem;
  letter-spacing: 0.12em; margin-top: 0.25rem;
  transition: border-color 0.2s, box-shadow 0.2s;
}
.dna-controls input[type="text"]:focus {
  border-color: var(--accent-primary); outline: none;
  box-shadow: 0 0 0 3px var(--ring-2);
}

/* ===== ECOSYSTEM ===== */
.eco-layout { display: grid; grid-template-columns: 1fr 300px; gap: 1.5rem; }
.eco-canvas-wrap {
  background: var(--canvas-bg); border: 1px solid var(--border-color);
  border-radius: 16px; overflow: hidden; box-shadow: var(--shadow-sm);
}
.eco-canvas-wrap canvas { display: block; width: 100%; height: auto; cursor: crosshair; }
.eco-controls {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 16px; padding: 1.5rem; box-shadow: var(--shadow-xs);
}
.species-palette {
  display: grid; grid-template-columns: repeat(2, 1fr); gap: 0.45rem; margin: 0.85rem 0;
}
.species-btn {
  padding: 0.45rem; border-radius: 10px; border: 1.5px solid var(--border-color);
  background: var(--bg-tertiary); cursor: grab; font-size: 0.8rem;
  text-align: center; font-family: inherit; transition: all 0.2s;
  color: var(--text-primary); font-weight: 500;
}
.species-btn:hover { border-color: var(--accent-biology); background: var(--success-soft); }
.species-btn.selected { border-color: var(--accent-biology); background: var(--accent-biology); color: #fff; }

.pop-chart { margin-top: 0.85rem; }
.pop-bar-row { display: flex; align-items: center; gap: 0.5rem; margin: 0.3rem 0; font-size: 0.75rem; }
.pop-bar { height: 16px; border-radius: 8px; transition: width 0.3s; min-width: 4px; }

/* ===== PERIODIC TABLE ===== */
.pt-controls-row {
  display: flex; gap: 0.75rem; margin-bottom: 1.25rem; flex-wrap: wrap;
}
#pt-search {
  flex: 1; min-width: 180px; padding: 0.5rem 0.85rem; border-radius: 10px;
  border: 1px solid var(--border-color); background: var(--input-bg);
  color: var(--text-primary); font-size: 0.875rem; font-family: inherit;
  transition: border-color 0.2s, box-shadow 0.2s;
}
#pt-search:focus { border-color: var(--accent-primary); outline: none; box-shadow: 0 0 0 3px var(--ring-2); }
#pt-filter {
  padding: 0.5rem 0.85rem; border-radius: 10px;
  border: 1px solid var(--border-color); background: var(--input-bg);
  color: var(--text-primary); font-size: 0.875rem; font-family: inherit;
}
.periodic-table-grid {
  display: grid; grid-template-columns: repeat(18, 1fr);
  gap: 2px; margin-bottom: 1.25rem;
}
.pt-cell {
  aspect-ratio: 1; display: flex; flex-direction: column;
  align-items: center; justify-content: center;
  border-radius: 6px; cursor: pointer; font-size: 0.65rem;
  padding: 2px; transition: transform 0.2s cubic-bezier(.22,.68,0,1.2), box-shadow 0.2s;
  border: 1px solid transparent; position: relative;
  color: #fff;
}
.pt-cell:hover { transform: scale(1.4); z-index: 10; box-shadow: var(--shadow-lg); }
.pt-cell .pt-num { font-size: 0.5rem; opacity: 0.8; }
.pt-cell .pt-sym { font-weight: 700; font-size: 0.85rem; line-height: 1.1; }
.pt-cell .pt-name { font-size: 0.4rem; opacity: 0.7; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; max-width: 100%; }
.pt-cell.dimmed { opacity: 0.12; }
.pt-placeholder { visibility: hidden; }

/* Element category colors — modern palette */
.cat-alkali-metal { background: #e11d48; }
.cat-alkaline-earth { background: #dc2626; }
.cat-transition-metal { background: #ea580c; }
.cat-post-transition-metal { background: #475569; }
.cat-metalloid { background: #0d9488; }
.cat-nonmetal { background: #16a34a; }
.cat-halogen { background: #0891b2; }
.cat-noble-gas { background: #7c3aed; }
.cat-lanthanide { background: #4338ca; }
.cat-actinide { background: #78350f; }
.cat-unknown { background: #6b7280; }

/* Element detail panel */
.element-detail-panel {
  position: fixed; top: 50%; left: 50%; transform: translate(-50%, -50%);
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 20px; padding: 2.25rem; z-index: 1000;
  box-shadow: var(--shadow-xl); max-width: 440px; width: 92%;
  animation: fadeIn 0.2s ease;
}
.close-btn {
  position: absolute; top: 1rem; right: 1.25rem;
  background: var(--bg-tertiary); border: 1px solid var(--border-color);
  width: 32px; height: 32px; border-radius: 8px; font-size: 1.25rem;
  cursor: pointer; color: var(--text-muted); transition: all 0.2s;
  display: flex; align-items: center; justify-content: center;
}
.close-btn:hover { color: var(--text-primary); background: var(--border-color); }
.element-detail-content .el-symbol { font-size: 3rem; font-weight: 800; }
.element-detail-content .el-name { font-size: 1.5rem; font-weight: 700; margin-bottom: 0.75rem; }
.el-props { list-style: none; padding: 0; }
.el-props li { padding: 0.4rem 0; font-size: 0.9rem; color: var(--text-secondary); border-bottom: 1px solid var(--border-color); }
.el-props li strong { color: var(--text-primary); }

/* ===== MOLECULES ===== */
.mol-layout { display: grid; grid-template-columns: 1fr 300px; gap: 1.5rem; }
.mol-canvas-wrap {
  background: var(--canvas-bg); border: 1px solid var(--border-color);
  border-radius: 16px; overflow: hidden; box-shadow: var(--shadow-sm);
}
.mol-canvas-wrap canvas { display: block; width: 100%; height: auto; cursor: grab; }
.mol-controls {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 16px; padding: 1.5rem; box-shadow: var(--shadow-xs);
}
.mol-controls select {
  width: 100%; padding: 0.55rem 0.75rem; border-radius: 10px;
  border: 1px solid var(--border-color); background: var(--input-bg);
  color: var(--text-primary); font-size: 0.9rem; margin: 0.5rem 0;
  font-family: inherit;
}
.hint { font-size: 0.8rem; color: var(--text-muted); font-style: italic; margin: 0.6rem 0; }

/* ===== PH SCALE ===== */
.ph-layout {
  display: grid; grid-template-columns: 1fr 1fr; gap: 1.75rem;
  align-items: start;
}
.ph-scale-visual { text-align: center; }
.ph-bar {
  height: 50px; border-radius: 14px; margin-bottom: 1.25rem;
  background: linear-gradient(to right,
    #ef4444, #f97316, #eab308, #84cc16, #22c55e,
    #14b8a6, #06b6d4, #3b82f6, #6366f1, #8b5cf6,
    #a855f7, #c026d3, #db2777, #e11d48, #881337
  );
  position: relative; box-shadow: var(--shadow-sm);
}
.ph-bar::after {
  content: ''; position: absolute; top: -5px; bottom: -5px;
  width: 4px; background: var(--text-primary); border-radius: 2px;
  left: 50%; transform: translateX(-50%);
  transition: left 0.2s;
  box-shadow: 0 0 8px rgba(0,0,0,0.3);
}
#ph-slider { width: 100%; margin: 0.5rem 0; accent-color: var(--accent-primary); }
.ph-value-display { font-size: 1.75rem; font-weight: 800; margin: 0.5rem 0; letter-spacing: -0.02em; }
.ph-info-panel {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 16px; padding: 1.75rem; box-shadow: var(--shadow-xs);
}
.ph-info-panel h3 { margin-bottom: 0.6rem; }
.ph-examples { margin: 1rem 0; }
.ph-example-item { display: flex; justify-content: space-between; padding: 0.4rem 0; font-size: 0.85rem; border-bottom: 1px solid var(--border-color); }

/* Beaker */
.beaker {
  width: 100px; height: 130px; margin: 1.25rem auto 0;
  border: 3px solid var(--text-muted); border-top: none;
  border-radius: 0 0 14px 14px; position: relative; overflow: hidden;
}
.liquid {
  position: absolute; bottom: 0; left: 0; right: 0;
  height: 80%; transition: background-color 0.3s;
  background: #00ff00;
}

/* ===== QUIZ ===== */
.quiz-container { max-width: 660px; margin: 0 auto; }
.quiz-header { text-align: center; margin-bottom: 1.75rem; }
.quiz-progress { display: flex; gap: 5px; margin: 1rem 0; justify-content: center; }
.quiz-dot {
  width: 12px; height: 12px; border-radius: 50%;
  background: var(--bg-tertiary); border: 1.5px solid var(--border-color);
  transition: all 0.2s;
}
.quiz-dot.correct { background: var(--success); border-color: var(--success); box-shadow: 0 0 6px var(--success-soft); }
.quiz-dot.wrong { background: var(--danger); border-color: var(--danger); box-shadow: 0 0 6px var(--danger-soft); }
.quiz-dot.current { border-color: var(--accent-primary); border-width: 2.5px; box-shadow: 0 0 6px var(--ring-1); }
.quiz-question {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 16px; padding: 1.75rem; margin-bottom: 1.25rem;
  box-shadow: var(--shadow-xs);
}
.quiz-question h3 { margin-bottom: 1.15rem; font-size: 1.1rem; line-height: 1.5; }
.quiz-options { display: flex; flex-direction: column; gap: 0.6rem; }
.quiz-option {
  padding: 0.85rem 1.15rem; border-radius: 12px; border: 1.5px solid var(--border-color);
  background: var(--bg-tertiary); cursor: pointer; font-size: 0.9rem;
  transition: all 0.2s; font-family: inherit; text-align: left;
  color: var(--text-primary); font-weight: 500;
}
.quiz-option:hover { border-color: var(--accent-primary); background: var(--accent-subtle); }
.quiz-option.selected { border-color: var(--accent-primary); background: var(--accent-primary); color: #fff; }
.quiz-option.correct { border-color: var(--success); background: var(--success-soft); color: var(--success); font-weight: 600; }
.quiz-option.wrong { border-color: var(--danger); background: var(--danger-soft); color: var(--danger); font-weight: 600; }
.quiz-result {
  text-align: center; padding: 2.5rem;
  background: var(--bg-card); border: 1px solid var(--border-color); border-radius: 16px;
  box-shadow: var(--shadow-sm);
}
.quiz-result h2 { margin-bottom: 0.6rem; }
.quiz-score { font-size: 3.5rem; font-weight: 800; color: var(--accent-primary); letter-spacing: -0.03em; }

/* Quiz explanation */
.quiz-explanation {
  margin-top: 1rem; padding: 1rem 1.15rem;
  background: var(--info-soft, var(--accent-subtle)); border: 1px solid var(--info, var(--accent-primary));
  border-radius: 10px; font-size: 0.85rem; line-height: 1.6;
  color: var(--text-secondary);
  animation: fadeIn 0.3s ease;
}
.quiz-explanation strong { color: var(--text-primary); }

/* ===== DASHBOARD ===== */
.dashboard-grid {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 1.5rem;
}
.dash-card {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 16px; padding: 1.75rem;
  box-shadow: var(--shadow-xs);
}
.dash-card.full-width { grid-column: 1 / -1; }
.dash-card h3 { margin-bottom: 1.15rem; font-size: 1.1rem; }
.progress-ring-wrap { text-align: center; position: relative; }
.progress-pct {
  position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%);
  font-size: 1.85rem; font-weight: 800; color: var(--accent-primary);
}
.module-progress-list { display: flex; flex-direction: column; gap: 0.85rem; }
.mod-prog-row { display: flex; align-items: center; gap: 0.85rem; }
.mod-prog-label { width: 110px; font-size: 0.85rem; font-weight: 600; }
.mod-prog-bar {
  flex: 1; height: 10px; background: var(--bg-tertiary);
  border-radius: 5px; overflow: hidden;
}
.mod-prog-fill { height: 100%; border-radius: 5px; transition: width 0.4s; }
.mod-prog-val { width: 40px; text-align: right; font-size: 0.8rem; color: var(--text-muted); font-weight: 600; }

.bookmarks-list, .quiz-scores-list { font-size: 0.9rem; }
.bookmark-item, .score-item {
  display: flex; align-items: center; justify-content: space-between;
  padding: 0.6rem 0; border-bottom: 1px solid var(--border-color);
}
.empty-state { color: var(--text-secondary); font-style: italic; font-size: 0.9rem; text-align: center; padding: 1.5rem 1rem; }

/* ===== TOOLTIP ===== */
.tooltip {
  position: fixed; z-index: 9999;
  background: var(--bg-card); border: 1px solid var(--border-color);
  box-shadow: var(--shadow-lg); border-radius: 10px;
  padding: 0.6rem 0.85rem; font-size: 0.8rem; max-width: 280px;
  pointer-events: none;
}

/* ===== FOOTER ===== */
.site-footer {
  margin-top: auto; padding: 2.5rem 1.5rem 2rem;
  color: var(--text-muted); font-size: 0.82rem;
  border-top: 1px solid var(--border-color);
  background: var(--bg-secondary);
}
.footer-inner {
  max-width: 1200px; margin: 0 auto;
  display: flex; flex-wrap: wrap; align-items: center;
  justify-content: space-between; gap: 1rem;
}
.footer-brand {
  display: flex; flex-direction: column; gap: 0.2rem;
}
.footer-brand strong {
  font-size: 1rem; color: var(--text-primary); font-weight: 700;
}
.footer-brand span { font-size: 0.78rem; }
.footer-links {
  display: flex; flex-wrap: wrap; gap: 0.5rem 1.25rem;
}
.footer-link {
  color: var(--text-secondary); text-decoration: none; font-size: 0.82rem;
  transition: color 0.2s;
}
.footer-link:hover { color: var(--accent-primary); }
.footer-meta {
  display: flex; gap: 1.25rem; font-size: 0.76rem; opacity: 0.7;
}
@media (max-width: 640px) {
  .footer-inner { flex-direction: column; text-align: center; }
  .footer-links { justify-content: center; }
  .footer-meta { justify-content: center; }
}

/* ===== CANVAS OVERLAY ===== */
.canvas-overlay {
  position: absolute; top: 10px; left: 10px;
  font-size: 0.75rem; color: var(--text-secondary);
  pointer-events: none;
}

/* ===== TOAST NOTIFICATIONS ===== */
.toast-container {
  position: fixed; bottom: 1.5rem; right: 1.5rem; z-index: 9999;
  display: flex; flex-direction: column-reverse; gap: 0.6rem;
  pointer-events: none;
}
.toast {
  background: var(--bg-card); border: 1px solid var(--border-color);
  border-radius: 12px; padding: 0.85rem 1.25rem;
  box-shadow: var(--shadow-lg); font-size: 0.875rem;
  display: flex; align-items: center; gap: 0.6rem;
  animation: toastIn 0.35s cubic-bezier(.22,.68,0,1.2);
  pointer-events: auto; max-width: 340px;
  font-weight: 500; color: var(--text-primary);
}
.toast.toast-out {
  animation: toastOut 0.3s ease forwards;
}
.toast-icon { font-size: 1.15rem; flex-shrink: 0; }
.toast-success { border-left: 4px solid var(--success); }
.toast-error { border-left: 4px solid var(--danger); }
.toast-info { border-left: 4px solid var(--info); }
.toast-warning { border-left: 4px solid var(--warning); }
@keyframes toastIn {
  from { opacity: 0; transform: translateY(20px) scale(0.95); }
  to { opacity: 1; transform: translateY(0) scale(1); }
}
@keyframes toastOut {
  from { opacity: 1; transform: translateY(0) scale(1); }
  to { opacity: 0; transform: translateY(10px) scale(0.95); }
}

/* ===== BACK TO TOP ===== */
.back-to-top {
  position: fixed; bottom: 1.5rem; right: 1.5rem; z-index: 950;
  width: 42px; height: 42px; border-radius: 50%;
  background: var(--accent-primary); color: #fff; border: none;
  cursor: pointer; font-size: 1.2rem; display: flex;
  align-items: center; justify-content: center;
  box-shadow: 0 4px 12px var(--accent-glow);
  opacity: 0; transform: translateY(10px);
  transition: opacity 0.3s, transform 0.3s;
  pointer-events: none;
}
.back-to-top.visible {
  opacity: 1; transform: translateY(0); pointer-events: auto;
}
.back-to-top:hover { transform: translateY(-2px); box-shadow: 0 6px 20px var(--accent-glow); }

/* ===== UTILITY ===== */
.hidden { display: none !important; }
.page { display: none; }
.page.active { display: block; animation: fadeIn 0.3s ease; }

/* ===== SCROLLBAR ===== */
::-webkit-scrollbar { width: 8px; height: 8px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border-color); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: var(--text-muted); }

/* ===== SELECTION ===== */
::selection { background: var(--accent-primary); color: #fff; }

/* ===== FOCUS RING ===== */
:focus-visible { outline: 2px solid var(--accent-primary); outline-offset: 2px; }
input:focus-visible, select:focus-visible, button:focus-visible { outline-offset: 1px; }