:root {
  --bg: #f3f4ff;
  --surface: #ffffff;
  --surface-alt: #eef0ff;
  --border: #d4d7ff;
  --accent: #4f46e5;
  --accent-strong: #4338ca;
  --accent-soft: #eef2ff;
  --text-main: #111827;
  --text-muted: #6b7280;
  --shadow: 0 18px 54px rgba(79, 70, 229, 0.12);
  --radius: 20px;
  --radius-sm: 12px;
  --transition: 0.2s ease;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: Inter, system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  background: linear-gradient(180deg, #eef1ff 0%, #f8fafc 100%);
  color: var(--text-main);
}

a {
  color: inherit;
  text-decoration: none;
}

button,
input,
select {
  font: inherit;
}

.navbar {
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(255,255,255,0.95);
  border-bottom: 1px solid rgba(79,70,229,0.08);
  backdrop-filter: blur(12px);
}

.nav-inner {
  max-width: 1180px;
  margin: 0 auto;
  padding: 16px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.nav-logo {
  font-size: 1.1rem;
  font-weight: 800;
  color: var(--accent);
}

.nav-links {
  display: flex;
  gap: 14px;
  flex-wrap: wrap;
}

.nav-links a {
  color: var(--text-muted);
  font-size: 0.95rem;
  padding: 8px 12px;
  border-radius: 999px;
  transition: background var(--transition), color var(--transition);
}

.nav-links a:hover {
  background: var(--accent-soft);
  color: var(--accent-strong);
}

.page-shell {
  max-width: 1180px;
  margin: 0 auto;
  padding: 28px 24px 60px;
  display: grid;
  grid-template-columns: minmax(0, 1.5fr) minmax(320px, 0.8fr);
  gap: 28px;
}

.tool-hero,
.tool-overview,
.tool-panel,
.learning-section,
.compare-section,
.trend-section {
  background: var(--surface);
  border: 1px solid rgba(79,70,229,0.08);
  border-radius: var(--radius);
  padding: 28px;
  box-shadow: var(--shadow);
}

.tool-hero {
  grid-column: 1 / -1;
  display: grid;
  grid-template-columns: 1.2fr 0.8fr;
  gap: 24px;
  align-items: center;
}

.hero-copy h1 {
  font-size: clamp(2.6rem, 3.8vw, 4.4rem);
  margin: 12px 0 18px;
  line-height: 1.02;
}

.hero-copy p {
  color: var(--text-muted);
  max-width: 600px;
  line-height: 1.75;
}

.hero-tag {
  display: inline-flex;
  background: #eef2ff;
  color: var(--accent-strong);
  padding: 8px 14px;
  border-radius: 999px;
  font-size: 0.9rem;
  font-weight: 700;
}

.hero-actions {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  margin-top: 24px;
}

.btn {
  border: none;
  cursor: pointer;
  border-radius: 999px;
  padding: 14px 22px;
  font-weight: 700;
  transition: transform var(--transition), box-shadow var(--transition);
}

.btn-primary {
  background: var(--accent);
  color: #fff;
}

.btn-secondary {
  background: #eef2ff;
  color: var(--accent-strong);
}

.btn:hover {
  transform: translateY(-1px);
}

.hero-visual {
  display: grid;
  gap: 18px;
}

.hero-card {
  background: #f8fafc;
  border-radius: 24px;
  padding: 24px;
  border: 1px solid rgba(79,70,229,0.09);
}

.hero-card span {
  display: block;
  color: var(--accent);
  font-size: 0.9rem;
  font-weight: 700;
}

.hero-card strong {
  display: block;
  margin-top: 12px;
  font-size: 1.1rem;
  line-height: 1.4;
}

.accent-card {
  background: linear-gradient(180deg, #eef2ff 0%, #eef4ff 100%);
}

.tool-overview {
  grid-column: 1 / -1;
}

.overview-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 18px;
  margin-top: 24px;
}

.overview-card {
  background: var(--surface-alt);
  border-radius: 18px;
  padding: 22px;
  border: 1px solid rgba(79,70,229,0.08);
}

.overview-card h3 {
  margin-bottom: 10px;
}

.tool-panel {
  grid-column: 1 / -1;
}

.panel-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.control-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 16px;
  margin: 24px 0 20px;
}

.control-field {
  display: grid;
  gap: 8px;
  font-size: 0.95rem;
}

.control-field input,
.control-field select {
  width: 100%;
  border-radius: 14px;
  border: 1px solid rgba(79,70,229,0.12);
  padding: 14px 16px;
  outline: none;
  background: #fff;
}

.control-field input:focus,
.control-field select:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 4px rgba(79,70,229,0.08);
}

.table-wrapper {
  border-radius: 24px;
  overflow-x: auto;
  overflow-y: hidden;
  border: 1px solid rgba(79,70,229,0.12);
  background: linear-gradient(180deg, #ffffff 0%, #f8f9ff 100%);
}

.table-grid {
  display: grid;
  grid-template-columns: repeat(18, minmax(44px, 1fr));
  grid-template-rows: repeat(9, minmax(0, auto));
  gap: 10px;
  padding: 18px;
  min-width: 760px;
}

.element-cell {
  min-height: 88px;
  aspect-ratio: 1 / 1;
  border-radius: 16px;
  padding: 10px;
  background: #fff;
  border: 1px solid rgba(79,70,229,0.08);
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  gap: 4px;
  text-align: center;
  position: relative;
  cursor: pointer;
  transition: transform var(--transition), box-shadow var(--transition), border-color var(--transition), background var(--transition);
}

.element-cell:hover,
.element-cell:focus-visible {
  transform: translateY(-2px);
  border-color: var(--accent);
  box-shadow: 0 10px 24px rgba(79, 70, 229, 0.12);
}

.element-cell.selected {
  border-color: var(--accent-strong);
  outline: 3px solid rgba(79, 70, 229, 0.22);
  box-shadow: 0 0 0 2px rgba(255,255,255,0.85), 0 14px 28px rgba(79, 70, 229, 0.2);
  transform: translateY(-2px) scale(1.01);
  background: linear-gradient(135deg, #ffffff 0%, #f5f7ff 100%);
}

.element-cell.selected::before {
  content: '';
  position: absolute;
  inset: 0;
  border-radius: inherit;
  border: 2px solid rgba(67, 56, 202, 0.32);
  pointer-events: none;
}

.element-cell.small {
  min-height: 74px;
}

.element-cell span {
  display: block;
  font-size: 0.8rem;
  color: var(--text-muted);
  line-height: 1.2;
}

.element-symbol {
  font-size: clamp(1rem, 1.8vw, 1.35rem);
  font-weight: 800;
  color: var(--text-main);
}

.element-number,
.element-mass {
  font-size: 0.78rem;
}

.element-name {
  font-size: clamp(0.74rem, 1.2vw, 0.9rem);
  font-weight: 600;
  color: var(--text-main);
}

.element-legend {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 10px;
  margin-top: 24px;
}

.legend-chip {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  border-radius: 999px;
  background: var(--surface-alt);
  padding: 12px 14px;
  font-size: 0.9rem;
}

.legend-key {
  width: 14px;
  height: 14px;
  border-radius: 50%;
  display: inline-block;
}

.detail-panel {
  background: var(--surface);
  border: 1px solid rgba(79,70,229,0.08);
  border-radius: var(--radius);
  padding: 24px;
  overflow: hidden;
}

@media (max-width: 1100px) {
  .page-shell {
    grid-template-columns: 1fr;
  }

  .tool-hero {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 720px) {
  .page-shell {
    padding: 18px 14px 42px;
  }

  .tool-hero,
  .tool-overview,
  .tool-panel,
  .learning-section,
  .compare-section,
  .trend-section,
  .detail-panel {
    padding: 20px;
  }

  .panel-head {
    flex-direction: column;
    align-items: flex-start;
  }

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

  .table-grid {
    gap: 8px;
    padding: 12px;
    min-width: 620px;
  }

  .element-cell {
    min-height: 72px;
    padding: 8px;
    border-radius: 12px;
  }

  .element-name {
    font-size: 0.72rem;
  }

  .detail-summary {
    grid-template-columns: 1fr 1fr;
  }
}

.detail-head {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.detail-category {
  color: var(--accent);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  font-size: 0.8rem;
  font-weight: 700;
}

.detail-summary {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
  margin-top: 22px;
}

.detail-card {
  background: var(--surface-alt);
  border-radius: 18px;
  padding: 18px;
}

.detail-card span {
  display: block;
  color: var(--text-muted);
  margin-bottom: 10px;
}

.detail-card strong {
  font-size: 1.05rem;
}

.detail-tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin: 24px 0 18px;
}

.tab-button {
  border: 1px solid rgba(79,70,229,0.14);
  background: #fff;
  color: var(--text-main);
  padding: 12px 16px;
  border-radius: 999px;
  cursor: pointer;
  transition: background var(--transition), color var(--transition);
}

.tab-button.active {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
}

.tab-panels {
  display: grid;
  gap: 20px;
}

.tab-panel {
  display: none;
}

.tab-panel.active {
  display: block;
}

.detail-list {
  list-style: none;
  padding: 0;
  margin: 0;
  display: grid;
  gap: 12px;
}

.detail-list li {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 16px;
  padding: 14px 18px;
  border-radius: 14px;
  background: var(--surface-alt);
}

.detail-list span {
  color: var(--text-muted);
  font-size: 0.95rem;
}

.detail-list strong {
  font-weight: 700;
}

.visual-blocker {
  display: grid;
  gap: 16px;
  margin-top: 20px;
}

.bohr-model {
  min-height: 220px;
  border-radius: 20px;
  background: radial-gradient(circle at top, rgba(79,70,229,0.12), transparent 45%), #f8f9ff;
  display: grid;
  place-items: center;
  position: relative;
}

.bohr-model::before,
.bohr-model::after {
  content: '';
  position: absolute;
  inset: 0;
  border-radius: 50%;
  opacity: 0.5;
}

.bohr-model::before {
  box-shadow: inset 0 0 0 3px rgba(79,70,229,0.15);
}

.orbital-preview {
  background: var(--surface-alt);
  border-radius: 18px;
  padding: 18px;
}

.state-card {
  background: #eef2ff;
  border-radius: 18px;
  padding: 20px;
}

.state-label {
  display: block;
  color: var(--accent-strong);
  font-size: 0.9rem;
  margin-bottom: 10px;
}

.state-visual {
  min-height: 135px;
  background: linear-gradient(180deg, #fff 0%, #eef2ff 100%);
  border-radius: 18px;
}

.history-block {
  background: var(--surface-alt);
  padding: 20px;
  border-radius: 18px;
}

.uses-list {
  list-style: none;
  padding: 0;
  margin: 0;
  display: grid;
  gap: 12px;
}

.uses-list li::before {
  content: '•';
  color: var(--accent);
  margin-right: 10px;
}

.notes-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 26px;
}

.notes-actions .btn {
  width: min(100%, 220px);
}

.learning-section,
.compare-section,
.trend-section {
  grid-column: 1 / -1;
}

.learning-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 18px;
  margin-top: 22px;
}

.learning-card {
  background: var(--surface-alt);
  border-radius: 20px;
  padding: 24px;
}

.learning-card h3 {
  margin-top: 0;
}

.learning-buttons {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
  margin-top: 18px;
}

.small-btn {
  border: none;
  border-radius: 999px;
  padding: 10px 14px;
  background: #eef2ff;
  color: var(--accent-strong);
  cursor: pointer;
}

.quiz-choices {
  display: grid;
  gap: 10px;
  margin-top: 16px;
}

.quiz-choice {
  background: #fff;
  border: 1px solid rgba(79,70,229,0.1);
  border-radius: 14px;
  padding: 14px 16px;
  cursor: pointer;
  transition: background var(--transition), border-color var(--transition);
}

.quiz-choice:hover {
  background: #eef2ff;
  border-color: var(--accent);
}

.quiz-status,
.compare-count {
  color: var(--text-muted);
  margin-top: 12px;
}

.progress-card {
  min-height: 200px;
}

.progress-list {
  list-style: none;
  display: grid;
  gap: 12px;
  padding: 0;
  margin: 0;
}

.compare-panel {
  display: grid;
  gap: 18px;
}

.compare-actions {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
}

.compare-list {
  display: grid;
  gap: 10px;
}

.compare-item {
  padding: 14px 16px;
  border-radius: 16px;
  background: var(--surface-alt);
  display: flex;
  justify-content: space-between;
  gap: 12px;
}

.trend-grid {
  display: grid;
  gap: 18px;
  margin-top: 22px;
}

.trend-card {
  padding: 20px;
  background: var(--surface-alt);
  border-radius: 18px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

canvas {
  width: 100% !important;
  max-height: 420px;
  border-radius: 18px;
}

@media (max-width: 1100px) {
  .page-shell {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 780px) {
  .tool-hero {
    grid-template-columns: 1fr;
  }

  .nav-inner {
    flex-wrap: wrap;
  }

  .detail-summary {
    grid-template-columns: 1fr;
  }
}

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