/* Color/spacing tokens now live in css/tokens.css, loaded before this file. */

    html[data-theme="dark"] .sidebar-header {
      background: linear-gradient(135deg, #1e1b4b 0%, #0b1220 100%);
    }

    html[data-theme="dark"] #sidebar-toggle,
    html[data-theme="dark"] #theme-toggle,
    html[data-theme="dark"] .control-btn,
    html[data-theme="dark"] #graph-settings-btn {
      background-color: rgba(30, 41, 59, 0.85);
    }

    html[data-theme="dark"] #tooltip {
      background: rgba(30, 41, 59, 0.95);
    }
    
    html[data-theme="dark"] #hover-dot {
      box-shadow: 0 0 0 3px rgba(30, 41, 59, 0.8);
    }

    html[data-theme="dark"] .ac-dropdown {
      background: #1e293b;
      box-shadow: 0 8px 32px rgba(0, 0, 0, 0.4);
    }

    html[data-theme="dark"] .ac-item:hover,
    html[data-theme="dark"] .ac-item.ac-active {
      background: rgba(129, 140, 248, 0.15);
    }

    html[data-theme="dark"] .sidebar-actions {
      background-color: transparent;
    }

    /* Universal box-sizing reset now lives in css/tokens.css */

    body {
      font-family: 'Inter', sans-serif;
      background-color: var(--bg-space);
      color: var(--text-main);
      height: 100vh;
      height: 100dvh; /* stable on mobile when browser chrome shows/hides */
      overflow: hidden;
      display: flex;
    }

    /* ── Sidebar Layout ── */
    #sidebar {
      width: 380px;
      min-width: 340px;
      background-color: var(--sidebar-bg);
      border-right: 1px solid var(--border-color);
      display: flex;
      flex-direction: column;
      height: 100%;
      z-index: 10;
      box-shadow: 8px 0 24px rgba(0, 0, 0, 0.05);
      transition: width 0.3s ease, min-width 0.3s ease, transform 0.3s ease;
      overflow: hidden;
      flex-shrink: 0;
    }

    #sidebar.collapsed {
      width: 0;
      min-width: 0;
      box-shadow: none;
    }

    /* Toggle sidebar button on graph panel */
    #sidebar-toggle {
      position: absolute;
      left: 12px;
      top: 12px;
      z-index: 20;
      background: rgba(255, 255, 255, 0.9);
      border: 1px solid var(--border-color);
      color: var(--text-main);
      width: 40px;
      height: 40px;
      border-radius: var(--radius-md);
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      backdrop-filter: blur(8px);
      transition: background 0.2s, color 0.2s, transform 0.15s;
      box-shadow: var(--shadow-lg);
    }

    #sidebar-toggle:hover {
      background: var(--card-active);
      color: var(--accent);
    }

    #sidebar-toggle:active {
      transform: scale(0.95);
    }

    #theme-toggle {
      position: absolute;
      right: 60px;
      top: 12px;
      z-index: 20;
      background: rgba(255, 255, 255, 0.9);
      border: 1px solid var(--border-color);
      color: var(--text-main);
      width: 40px;
      height: 40px;
      border-radius: var(--radius-md);
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      backdrop-filter: blur(8px);
      transition: background 0.2s, color 0.2s, transform 0.15s;
      box-shadow: var(--shadow-lg);
    }

    #theme-toggle:hover {
      background: var(--card-active);
      color: var(--accent);
    }

    #theme-toggle:active {
      transform: scale(0.95);
    }

    .sidebar-header {
      padding: 16px 20px;
      border-bottom: 1px solid var(--border-color);
      background: linear-gradient(135deg, #e0e7ff 0%, #f8fafc 100%);
    }

    .logo-container {
      display: flex;
      align-items: center;
      gap: 12px;
    }

    .logo-home-link {
      display: flex;
      align-items: center;
      gap: 12px;
      text-decoration: none;
      color: inherit;
      min-width: 0;
    }

    .logo-icon {
      width: 28px;
      height: 28px;
      background: linear-gradient(135deg, #818cf8, #34d399);
      border-radius: 8px;
      display: flex;
      align-items: center;
      justify-content: center;
      font-weight: 800;
      color: #ffffff;
      font-size: 0.9rem;
    }

    .logo-img {
      height: 38px;
      width: auto;
      object-fit: contain;
    }

    .sidebar-header h1 {
      font-size: 1.5rem;
      font-weight: 750;
      letter-spacing: -0.03em;
      color: var(--text-main);
      line-height: 1;
      margin: 0;
      transform: translateY(-2px);
    }

    .howto-btn {
      margin-left: auto;
      background: rgba(255, 255, 255, 0.7);
      border: 1px solid var(--border-color);
      color: var(--text-muted);
      width: 26px;
      height: 26px;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      flex-shrink: 0;
      transition: background 0.2s, color 0.2s, border-color 0.2s;
    }

    .howto-btn:hover {
      color: var(--accent);
      border-color: var(--accent);
    }

    html[data-theme="dark"] .howto-btn {
      background: rgba(30, 41, 59, 0.6);
    }

    /* ── How the graph is built modal ── */
    .howto-overlay {
      position: fixed;
      inset: 0;
      background: rgba(15, 23, 42, 0.55);
      backdrop-filter: blur(4px);
      display: none;
      align-items: center;
      justify-content: center;
      z-index: 200;
      padding: 20px;
    }

    .howto-overlay.open {
      display: flex;
    }

    .howto-card {
      background: var(--card-bg);
      border: 1px solid var(--border-color);
      border-radius: var(--radius-lg);
      box-shadow: 0 20px 50px rgba(0, 0, 0, 0.25);
      width: min(880px, 100%);
      max-height: 90vh;
      display: flex;
      flex-direction: column;
      overflow: hidden;
    }

    .howto-card-header {
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 18px 22px;
      border-bottom: 1px solid var(--border-color);
    }

    .howto-card-header h2 {
      font-size: 1.05rem;
      font-weight: 700;
      color: var(--text-main);
    }

    .howto-steps {
      display: grid;
      grid-template-columns: repeat(4, 1fr);
      gap: 16px;
      padding: 24px;
      overflow-y: auto;
    }

    .howto-step {
      position: relative;
      background: var(--card-active);
      border: 1px solid var(--border-color);
      border-radius: var(--radius-md);
      padding: 20px 16px;
      text-align: center;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 8px;
    }

    .howto-num {
      position: absolute;
      top: 10px;
      left: 10px;
      width: 20px;
      height: 20px;
      border-radius: 50%;
      background: var(--accent);
      color: #fff;
      font-size: 0.7rem;
      font-weight: 700;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    .howto-icon {
      margin: 6px 0 4px;
    }

    .howto-step h3 {
      font-size: 0.92rem;
      font-weight: 700;
      color: var(--text-main);
    }

    .howto-step p {
      font-size: 0.78rem;
      color: var(--text-muted);
      line-height: 1.5;
    }

    .howto-step code {
      font-family: 'JetBrains Mono', monospace;
      background: rgba(99, 102, 241, 0.1);
      color: var(--accent);
      padding: 1px 5px;
      border-radius: 4px;
      font-size: 0.75rem;
    }

    .sidebar-header p {
      font-size: 0.75rem;
      color: var(--text-muted);
      margin-top: 4px;
      line-height: 1.4;
    }

    /* ── Equations List ── */
    .equations-container {
      flex-grow: 1;
      overflow-y: auto;
      padding: 16px;
      display: flex;
      flex-direction: column;
      gap: 10px;
    }

    .eq-card {
      background-color: var(--card-bg);
      border: 1px solid var(--border-color);
      border-radius: var(--radius-md);
      padding: 12px;
      display: flex;
      flex-direction: column;
      gap: 10px;
      transition: transform 0.2s, border-color 0.2s, box-shadow 0.2s;
    }

    .eq-card:hover {
      border-color: var(--border-color);
    }

    .eq-card.active-focus {
      border-color: var(--border-color);
    }

    .eq-card.error {
      border-color: var(--danger);
    }

    .eq-row {
      display: flex;
      align-items: center;
      gap: 10px;
    }

    .eq-input-wrapper {
      flex-grow: 1;
      position: relative;
      display: flex;
      align-items: center;
    }

    .eq-input {
      width: 100%;
      background-color: var(--input-bg);
      border: 1px solid var(--border-color);
      border-radius: var(--radius-sm);
      padding: 9px 12px;
      color: var(--text-main);
      font-family: 'JetBrains Mono', monospace;
      font-size: 0.9rem;
      outline: none;
      transition: border-color 0.2s, box-shadow 0.2s;
    }

    .eq-input:focus {
      border-color: var(--border-color);
    }

    .eq-input:focus-visible,
    .pp-eq-row input:focus-visible,
    .pp-x-input:focus-visible,
    .pp-active-eq-select:focus-visible {
      outline: none;
    }

    .btn-icon {
      background: none;
      border: none;
      color: var(--text-muted);
      cursor: pointer;
      padding: 6px;
      border-radius: 6px;
      display: flex;
      align-items: center;
      justify-content: center;
      transition: background-color 0.2s, color 0.2s;
    }

    .btn-icon:hover {
      background-color: rgba(255, 255, 255, 0.06);
      color: var(--text-main);
    }

    .btn-icon.delete:hover {
      background-color: rgba(239, 68, 68, 0.1);
      color: var(--danger);
    }

    .btn-icon.plot-target:hover {
      background-color: rgba(245, 158, 11, 0.08);
      color: #f59e0b;
    }

    .btn-icon.plot-target.active {
      color: #f59e0b;
      background-color: rgba(245, 158, 11, 0.12);
    }

    .eq-error {
      font-size: 0.75rem;
      color: var(--danger);
      background-color: var(--danger-bg);
      padding: 6px 10px;
      border-radius: var(--radius-sm);
      margin-top: 4px;
      border: 1px solid rgba(239, 68, 68, 0.15);
      line-height: 1.4;
      display: none;
    }

    /* ── Point Plotter panel ── */
    .points-panel {
      flex-shrink: 0;
      border-top: 1px solid var(--border-color);
    }

    .points-panel-toggle {
      width: 100%;
      display: flex;
      align-items: center;
      justify-content: space-between;
      background: none;
      border: none;
      padding: 14px 20px;
      cursor: pointer;
      color: var(--text-main);
      font-family: inherit;
      font-size: 0.85rem;
      font-weight: 600;
      transition: background 0.15s;
    }

    .points-panel-toggle:hover { background: var(--card-active); }

    .points-panel-title {
      display: flex;
      align-items: center;
      gap: 8px;
    }

    .points-dot {
      width: 8px;
      height: 8px;
      border-radius: 50%;
      background: #f59e0b;
      flex-shrink: 0;
    }

    .points-chevron {
      color: var(--text-muted);
      transition: transform 0.2s;
    }

    .points-panel.collapsed .points-chevron { transform: rotate(-90deg); }
    .points-panel.collapsed .points-panel-body { display: none; }

    .points-panel-body {
      padding: 0 16px 16px;
      display: flex;
      flex-direction: column;
      gap: 12px;
    }

    /* Step blocks */
    .pp-step {
      display: flex;
      flex-direction: column;
      gap: 6px;
    }

    .pp-step-label {
      display: flex;
      align-items: center;
      gap: 6px;
      font-size: 0.7rem;
      font-weight: 700;
      letter-spacing: 0.06em;
      text-transform: uppercase;
      color: var(--text-muted);
    }

    .pp-step-num {
      width: 18px;
      height: 18px;
      border-radius: 50%;
      background: var(--accent);
      color: #fff;
      font-size: 0.65rem;
      font-weight: 800;
      display: flex;
      align-items: center;
      justify-content: center;
      flex-shrink: 0;
    }

    /* Equation row: input + ready badge */
    .pp-eq-row {
      display: flex;
      align-items: center;
      gap: 8px;
    }

    .pp-eq-row input {
      flex-grow: 1;
      min-width: 0;
      background-color: var(--input-bg);
      border: 1px solid var(--border-color);
      border-radius: var(--radius-sm);
      padding: 9px 12px;
      color: var(--text-main);
      font-family: 'JetBrains Mono', monospace;
      font-size: 0.85rem;
      outline: none;
      transition: border-color 0.2s, box-shadow 0.2s;
    }

    .pp-eq-row input:focus {
      border-color: var(--border-color);
      box-shadow: none;
    }

    .pp-eq-row input.pp-eq-ok {
      border-color: #10b981;
    }

    .pp-ready-badge {
      font-size: 0.65rem;
      font-weight: 700;
      padding: 3px 7px;
      border-radius: 999px;
      background: rgba(16,185,129,0.12);
      color: #10b981;
      border: 1px solid rgba(16,185,129,0.3);
      white-space: nowrap;
      display: none;
    }

    /* X input area */
    .pp-x-row {
      display: flex;
      align-items: center;
      gap: 8px;
      position: relative;
    }

    .pp-x-label {
      font-family: 'JetBrains Mono', monospace;
      font-size: 0.85rem;
      font-weight: 700;
      color: var(--text-muted);
      flex-shrink: 0;
    }

    .pp-x-input {
      flex-grow: 1;
      min-width: 0;
      background-color: var(--input-bg);
      border: 2px solid var(--accent);
      border-radius: var(--radius-sm);
      padding: 9px 90px 9px 12px;
      color: var(--text-main);
      font-family: 'JetBrains Mono', monospace;
      font-size: 0.95rem;
      outline: none;
      transition: box-shadow 0.2s;
    }

    .pp-x-input:focus {
      box-shadow: none;
    }

    .pp-plot-btn {
      flex-shrink: 0;
      background-color: var(--accent);
      color: #fff;
      border: none;
      border-radius: var(--radius-sm);
      padding: 9px 14px;
      font-size: 0.82rem;
      font-weight: 700;
      cursor: pointer;
      transition: background 0.15s, transform 0.1s;
      display: flex;
      align-items: center;
      gap: 5px;
      white-space: nowrap;
    }

    .pp-plot-btn:hover { background-color: var(--accent-hover); }
    .pp-plot-btn:active { transform: scale(0.95); }

    .pp-key-hint {
      font-size: 0.68rem;
      color: var(--text-muted);
      display: flex;
      align-items: center;
      gap: 4px;
    }

    .pp-key {
      display: inline-flex;
      align-items: center;
      background: var(--card-active);
      border: 1px solid var(--border-color);
      border-radius: 4px;
      padding: 1px 5px;
      font-family: 'JetBrains Mono', monospace;
      font-size: 0.65rem;
      font-weight: 600;
    }

    /* Points table */
    .pp-table {
      width: 100%;
      border-collapse: collapse;
      font-family: 'JetBrains Mono', monospace;
      font-size: 0.78rem;
    }

    .pp-table th {
      text-align: left;
      font-size: 0.65rem;
      text-transform: uppercase;
      letter-spacing: 0.06em;
      color: var(--text-muted);
      padding: 4px 8px;
      border-bottom: 1px solid var(--border-color);
    }

    .pp-table th:last-child { width: 28px; }

    .pp-table td {
      padding: 5px 8px;
      color: var(--text-main);
      border-bottom: 1px solid var(--border-color);
    }

    .pp-table tr:last-child td { border-bottom: none; }

    .pp-table tbody tr:nth-child(odd) td {
      background: var(--card-active);
    }

    .pp-table-wrap {
      border: 1px solid var(--border-color);
      border-radius: var(--radius-sm);
      overflow: hidden;
      max-height: 180px;
      overflow-y: auto;
    }

    .pp-table-footer {
      display: flex;
      align-items: center;
      justify-content: flex-end;
      height: 28px;
      margin-top: 6px;
    }

    .pp-clear-btn {
      background: none;
      border: 1px solid var(--border-color);
      border-radius: var(--radius-sm);
      color: var(--text-muted);
      font-size: 0.72rem;
      cursor: pointer;
      padding: 4px 8px;
      transition: all 0.15s;
    }

    .pp-clear-btn:hover:not(:disabled) {
      border-color: var(--danger);
      color: var(--danger);
      background-color: rgba(239, 68, 68, 0.05);
    }

    .pp-row-del {
      background: none;
      border: none;
      color: var(--text-muted);
      cursor: pointer;
      padding: 2px 4px;
      border-radius: 3px;
      line-height: 1;
    }

    .pp-row-del:hover { background: rgba(239,68,68,0.12); color: var(--danger); }

    .pp-error {
      font-size: 0.75rem;
      color: var(--danger);
      background-color: var(--danger-bg);
      padding: 5px 10px;
      border-radius: var(--radius-sm);
      border: 1px solid rgba(239,68,68,0.2);
      line-height: 1.4;
      display: none;
    }

    .pp-active-eq-container {
      display: flex;
      flex-direction: column;
      gap: 4px;
      margin-bottom: 8px;
    }

    .pp-select-wrapper {
      position: relative;
      width: 100%;
    }

    .pp-active-eq-select {
      appearance: none;
      -webkit-appearance: none;
      width: 100%;
      background-color: var(--card-active);
      border: 1px solid var(--border-color);
      border-radius: var(--radius-sm);
      padding: 8px 32px 8px 12px;
      color: var(--accent);
      font-family: 'JetBrains Mono', monospace;
      font-size: 0.85rem;
      font-weight: 600;
      outline: none;
      cursor: pointer;
      background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' fill='none' stroke='%236366f1' stroke-width='2.5' viewBox='0 0 24 24'%3E%3Cpolyline points='6 9 12 15 18 9'/%3E%3C/svg%3E");
      background-repeat: no-repeat;
      background-position: right 12px center;
      background-size: 14px;
      transition: border-color 0.15s, box-shadow 0.15s;
    }

    .pp-active-eq-select:focus {
      border-color: var(--border-color);
    }

    .pp-active-eq-select option {
      background-color: var(--card-bg);
      color: var(--text-main);
      font-family: 'JetBrains Mono', monospace;
    }

    .pp-no-eq {
      font-size: 0.78rem;
      color: var(--text-muted);
      text-align: center;
      padding: 12px 0;
      font-style: italic;
    }

    .pp-y-preview {
      position: absolute;
      right: 12px;
      font-family: 'JetBrains Mono', monospace;
      font-size: 0.85rem;
      font-weight: 600;
      pointer-events: none;
    }

    .sidebar-actions {
      padding: 20px;
      border-top: 1px solid var(--border-color);
      display: flex;
      gap: 12px;
      background-color: transparent;
    }

    .btn-primary {
      background-color: var(--text-main);
      color: var(--bg-space);
      border: none;
      padding: 12px 18px;
      border-radius: var(--radius-md);
      font-weight: 600;
      font-size: 0.9rem;
      cursor: pointer;
      transition: opacity 0.2s, transform 0.15s;
      flex-grow: 2;
      display: flex;
      justify-content: center;
      align-items: center;
      gap: 8px;
    }

    .btn-primary:hover {
      opacity: 0.9;
    }

    .btn-secondary {
      background-color: var(--card-bg);
      color: var(--text-main);
      border: 1px solid var(--border-color);
      padding: 12px 14px;
      border-radius: var(--radius-md);
      font-weight: 600;
      font-size: 0.85rem;
      cursor: pointer;
      transition: background 0.2s, transform 0.15s;
      flex-grow: 1;
      display: flex;
      justify-content: center;
      align-items: center;
      gap: 6px;
    }

    .btn-secondary:hover {
      background-color: var(--card-active);
    }

    .btn-secondary:active {
      transform: scale(0.97);
    }

    /* ── Graph Panel Layout ── */
    #graph-container {
      flex-grow: 1;
      height: 100%;
      position: relative;
      background-color: var(--bg-space);
    }

    canvas {
      display: block;
      width: 100%;
      height: 100%;
      touch-action: none;
    }

    /* ── Controls Overlay ── */
    .controls-overlay {
      position: absolute;
      right: 24px;
      bottom: 24px;
      display: flex;
      flex-direction: column;
      gap: 8px;
      z-index: 10;
    }

    .control-btn {
      background-color: rgba(255, 255, 255, 0.85);
      border: 1px solid var(--border-color);
      color: var(--text-main);
      width: 44px;
      height: 44px;
      border-radius: var(--radius-md);
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      backdrop-filter: blur(8px);
      transition: background-color 0.2s, border-color 0.2s, transform 0.15s;
      box-shadow: var(--shadow-lg);
    }

    .control-btn:hover {
      background-color: var(--card-active);
      border-color: var(--accent);
      color: var(--accent);
    }

    .control-btn:active {
      transform: scale(0.95);
    }

    /* ── Empty state (shown until the user interacts with the graph) ── */
    .empty-state {
      position: absolute;
      inset: 0;
      z-index: 6;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      gap: 10px;
      background-color: var(--bg-space);
      text-align: center;
      padding: 24px;
      color: var(--text-muted);
    }

    .empty-state.hidden {
      display: none;
    }

    .empty-state svg {
      color: var(--accent);
      opacity: 0.7;
      margin-bottom: 4px;
    }

    .empty-state h3 {
      font-size: 1rem;
      font-weight: 600;
      color: var(--text-main);
    }

    .empty-state p {
      font-size: 0.85rem;
      max-width: 280px;
    }

    /* ── Graph settings button + dropdown ── */
    #graph-settings-btn {
      position: absolute;
      right: 12px;
      top: 12px;
      z-index: 20;
      background: rgba(255, 255, 255, 0.9);
      border: 1px solid var(--border-color);
      color: var(--text-main);
      width: 40px;
      height: 40px;
      border-radius: var(--radius-md);
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      backdrop-filter: blur(8px);
      transition: background 0.2s, color 0.2s, transform 0.15s;
      box-shadow: var(--shadow-lg);
    }

    #graph-settings-btn:hover {
      background: var(--card-active);
      color: var(--accent);
    }

    #graph-settings-btn:active {
      transform: scale(0.95);
    }

    .settings-menu {
      position: absolute;
      right: 12px;
      top: 58px;
      z-index: 21;
      width: 220px;
      background: var(--card-bg);
      border: 1px solid var(--border-color);
      border-radius: var(--radius-md);
      box-shadow: 0 10px 30px rgba(0, 0, 0, 0.12);
      padding: 6px;
      display: none;
      flex-direction: column;
      gap: 2px;
    }

    .settings-menu.open {
      display: flex;
    }

    .settings-row {
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 8px 10px;
      border-radius: var(--radius-sm);
      font-size: 0.85rem;
      color: var(--text-main);
    }

    .settings-row:hover {
      background: var(--card-active);
    }

    .switch {
      position: relative;
      display: inline-block;
      width: 34px;
      height: 20px;
      flex-shrink: 0;
    }

    .switch input {
      opacity: 0;
      width: 0;
      height: 0;
    }

    .switch-slider {
      position: absolute;
      inset: 0;
      background-color: #cbd5e1;
      border-radius: 999px;
      cursor: pointer;
      transition: background-color 0.2s;
    }

    .switch-slider::before {
      content: "";
      position: absolute;
      width: 16px;
      height: 16px;
      left: 2px;
      top: 2px;
      background-color: #fff;
      border-radius: 50%;
      transition: transform 0.2s;
      box-shadow: 0 1px 3px rgba(0, 0, 0, 0.25);
    }

    .switch input:checked+.switch-slider {
      background-color: var(--accent);
    }

    .switch input:checked+.switch-slider::before {
      transform: translateX(14px);
    }

    .grid-style-row {
      display: flex;
      gap: 4px;
      background: var(--sidebar-bg);
      border-radius: var(--radius-sm);
      padding: 4px;
      margin: 4px 2px 2px;
    }

    .grid-style-btn {
      flex: 1;
      display: flex;
      align-items: center;
      justify-content: center;
      height: 32px;
      border: 1px solid transparent;
      border-radius: 6px;
      background: transparent;
      color: var(--text-muted);
      cursor: pointer;
      transition: background 0.15s, color 0.15s, border-color 0.15s;
    }

    .grid-style-btn:hover {
      color: var(--text-main);
    }

    .grid-style-btn.active {
      background: #e0e7ff;
      border-color: var(--accent);
      color: var(--accent);
    }

    html[data-theme="dark"] .grid-style-btn.active {
      background: rgba(129, 140, 248, 0.18);
    }

    .open-settings-link {
      margin-top: 4px;
      width: 100%;
      background: none;
      border: none;
      color: var(--accent);
      font-size: 0.85rem;
      font-weight: 600;
      text-align: center;
      padding: 8px 10px;
      cursor: pointer;
      border-radius: var(--radius-sm);
    }

    .open-settings-link:hover {
      background: var(--card-active);
      text-decoration: underline;
    }

    /* ── Autocomplete dropdown ── */
    .ac-dropdown {
      position: fixed;
      background: #fff;
      border: 1px solid var(--border-color);
      border-radius: 10px;
      box-shadow: 0 8px 32px rgba(0, 0, 0, 0.13);
      z-index: 9999;
      min-width: 230px;
      max-height: 320px;
      overflow-y: auto;
      display: none;
      flex-direction: column;
    }

    .ac-item {
      padding: 7px 14px;
      font-size: 0.85rem;
      font-family: 'JetBrains Mono', monospace;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 10px;
      transition: background 0.1s;
      color: var(--text-main);
    }

    .ac-item:hover,
    .ac-item.ac-active {
      background: #eef2ff;
      color: var(--accent);
    }

    .ac-item-main {
      display: flex;
      flex-direction: column;
      gap: 1px;
      min-width: 0;
      flex-grow: 1;
    }

    .ac-item-name {
      font-weight: 600;
      white-space: nowrap;
    }

    .ac-item-desc {
      font-family: 'Inter', sans-serif;
      font-size: 0.68rem;
      color: var(--text-muted);
      white-space: nowrap;
      overflow: hidden;
      text-overflow: ellipsis;
    }

    .ac-item-badge {
      font-size: 0.62rem;
      font-weight: 700;
      padding: 1px 5px;
      border-radius: 4px;
      text-transform: uppercase;
      letter-spacing: 0.04em;
      flex-shrink: 0;
    }

    .ac-badge-trig {
      background: #dbeafe;
      color: #2563eb;
    }

    .ac-badge-inv {
      background: #ede9fe;
      color: #7c3aed;
    }

    .ac-badge-hyp {
      background: #ccfbf1;
      color: #0d9488;
    }

    .ac-badge-ihyp {
      background: #fef3c7;
      color: #b45309;
    }

    .ac-badge-fn {
      background: #dcfce7;
      color: #059669;
    }

    .ac-badge-var {
      background: #f3e8ff;
      color: #7c3aed;
    }

    .ac-badge-op {
      background: #eef2ff;
      color: #4f46e5;
    }


    /* ── Hover Tooltip ── */
    #tooltip {
      position: absolute;
      pointer-events: none;
      background: rgba(255, 255, 255, 0.95);
      border: 2px solid var(--accent);
      color: var(--text-main);
      padding: 6px 12px;
      border-radius: var(--radius-sm);
      font-family: 'JetBrains Mono', monospace;
      font-size: 0.8rem;
      display: none;
      box-shadow: 0 4px 20px rgba(0, 0, 0, 0.08);
      z-index: 20;
    }

    #hover-dot {
      position: absolute;
      pointer-events: none;
      width: 12px;
      height: 12px;
      background: var(--bg-main);
      border: 2px solid var(--accent);
      border-radius: 50%;
      display: none;
      transform: translate(-50%, -50%);
      box-shadow: 0 0 0 3px rgba(255, 255, 255, 0.5);
      z-index: 19;
      transition: top 0.05s linear, left 0.05s linear;
    }

    /* ── Preview Modal (shown on Visualize, before entering interactive view) ── */
    .preview-overlay {
      position: fixed;
      inset: 0;
      background: rgba(15, 23, 42, 0.55);
      backdrop-filter: blur(4px);
      display: none;
      align-items: center;
      justify-content: center;
      z-index: 100;
    }

    .preview-overlay.open {
      display: flex;
    }

    .preview-card {
      background: var(--card-bg);
      border: 1px solid var(--border-color);
      border-radius: var(--radius-lg);
      box-shadow: 0 20px 50px rgba(0, 0, 0, 0.25);
      width: min(960px, 94vw);
      max-height: 92vh;
      display: flex;
      flex-direction: column;
      overflow: hidden;
    }

    .preview-card-header {
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 16px 20px;
      border-bottom: 1px solid var(--border-color);
    }

    .preview-card-header h2 {
      font-size: 1rem;
      font-weight: 700;
      color: var(--text-main);
    }

    .preview-card-body {
      padding: 16px 20px;
      overflow: auto;
      display: flex;
      justify-content: center;
      align-items: center;
      min-height: 420px;
      background-color: var(--bg-space);
    }

    .preview-card-body img {
      width: 100%;
      max-width: 100%;
      border-radius: var(--radius-sm);
      border: 1px solid var(--border-color);
      display: block;
    }

    .preview-card-actions {
      display: flex;
      gap: 12px;
      padding: 16px 20px;
      border-top: 1px solid var(--border-color);
    }



    /* Responsive & Mobile Queries */
    @media (max-width: 768px) {
      #sidebar {
        position: absolute;
        left: 0;
        top: 0;
        bottom: 0;
        z-index: 1000;
        width: 300px;
        min-width: 0;
        max-width: 85vw;
        box-shadow: 4px 0 25px rgba(0, 0, 0, 0.25);
        transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1), box-shadow 0.3s;
        transform: translateX(0);
      }

      #sidebar.collapsed {
        transform: translateX(-100%);
        box-shadow: none;
      }

      #graph-container {
        width: 100%;
        height: 100%;
        position: relative;
      }

      /* Adjust sidebar toggle position when sidebar is open vs collapsed */
      #sidebar-toggle {
        z-index: 1001;
        transition: background 0.2s, color 0.2s, transform 0.15s, left 0.3s cubic-bezier(0.4, 0, 0.2, 1);
      }

      #sidebar:not(.collapsed) + #graph-container #sidebar-toggle {
        left: calc(300px + 12px);
      }

      #sidebar.collapsed + #graph-container #sidebar-toggle {
        left: 12px;
      }

      /* Make touch targets larger and friendly on mobile */
      .btn-icon, 
      .control-btn, 
      #graph-settings-btn, 
      .pp-clear-btn, 
      .btn-primary, 
      #theme-toggle,
      #sidebar-toggle {
        min-height: 44px;
        min-width: 44px;
      }

      .eq-input {
        font-size: 1rem; /* prevent automatic iOS viewport zoom on input focus */
        padding: 10px 14px;
      }

      .eq-row {
        gap: 8px;
      }

      /* Control panel float layout spacing on mobile */
      .controls-overlay {
        bottom: 16px;
        right: 16px;
        gap: 10px;
      }

      .control-btn {
        width: 44px;
        height: 44px;
      }

      /* Floating settings menu adjustment */
      .settings-menu {
        top: 68px;
        right: 16px;
        left: 16px;
        width: auto;
        max-width: calc(100vw - 32px);
        box-shadow: var(--shadow-xl);
      }

      /* Point plotter mobile responsiveness */
      .points-panel.open {
        max-height: 250px;
      }

      .pp-table-container {
        max-height: 140px;
      }

      /* How it Works modal: stack to single column on mobile */
      .howto-steps {
        grid-template-columns: 1fr;
        padding: 16px;
        gap: 12px;
      }

      .howto-card {
        max-height: 85vh;
      }

      .howto-btn {
        min-height: 26px;
        min-width: 26px;
      }

      .mobile-sidebar-close {
        display: flex;
      }
    }

    @media (max-width: 480px) {
      #sidebar {
        width: 280px;
        max-width: 90vw;
      }
      
      #sidebar.collapsed {
        width: 0;
        min-width: 0;
        max-width: 0;
      }

      #sidebar:not(.collapsed) + #graph-container #sidebar-toggle {
        left: calc(280px + 12px);
      }

      .sidebar-header h1 {
        font-size: 1.3rem;
      }

      .logo-img {
        height: 32px;
      }
    }

    /* .mobile-sidebar-close is only meaningful on mobile, where the sidebar
       becomes a slide-in drawer; keep it out of the way on desktop. */
    .mobile-sidebar-close {
      display: none;
    }

    input:focus, select:focus, textarea:focus, button:focus {
      outline: none !important;
      box-shadow: none !important;
    }

    .no-transition {
      transition: none !important;
    }

    /* ── Feedback Button Styles ── */
    .feedback-btn {
      background: rgba(255, 255, 255, 0.7);
      border: 1px solid var(--border-color);
      color: var(--text-muted);
      width: 28px;
      height: 28px;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      flex-shrink: 0;
      transition: background 0.2s, color 0.2s, border-color 0.2s;
    }

    .feedback-btn:hover {
      color: var(--accent);
      border-color: var(--accent);
      background-color: var(--card-active);
    }

    html[data-theme="dark"] .feedback-btn {
      background: rgba(30, 41, 59, 0.6);
    }