/* ── Right Panel ── */
    #right-panel {
      width: var(--right-width);
      background: var(--surface-low);
      display: flex;
      flex-direction: column;
      overflow: hidden;
      flex-shrink: 0;
    }

    .rp-tabs {
      display: flex;
      background: var(--surface-highest);
      flex-shrink: 0;
    }

    .rp-tab {
      flex: 1;
      padding: 0.65rem 0.2rem;
      font-size: 0.63rem;
      font-weight: 700;
      letter-spacing: 0.06em;
      text-transform: uppercase;
      color: var(--outline);
      cursor: pointer;
      border-bottom: 2.5px solid transparent;
      text-align: center;
      transition: all var(--dur-fast);
    }

    .rp-tab:hover {
      color: var(--on-surface);
    }

    .rp-tab.active {
      color: var(--primary);
      border-bottom-color: var(--primary);
      background: var(--surface-lowest);
    }

    .rp-content {
      flex: 1;
      overflow-y: auto;
      padding: 1rem;
    }

    .rp-pane {
      display: none;
    }

    .rp-pane.active {
      display: block;
    }

    /* Explanation cards */
    .exp-card {
      background: var(--surface-lowest);
      border-radius: var(--radius-xl);
      padding: 1rem;
      margin-bottom: 0.75rem;
      box-shadow: var(--ambient-shadow);
    }

    .exp-step-badge {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      width: 26px;
      height: 26px;
      background: var(--primary);
      border-radius: var(--radius-full);
      font-size: 0.72rem;
      font-weight: 700;
      color: white;
      margin-bottom: 0.5rem;
    }

    .exp-title {
      font-family: 'Manrope', sans-serif;
      font-size: 0.95rem;
      font-weight: 700;
      color: var(--on-surface);
      margin-bottom: 0.35rem;
    }

    .exp-desc {
      font-size: 0.78rem;
      color: var(--on-surface-variant);
      line-height: 1.55;
    }

    .exp-diagram {
      margin: 0.5rem 0;
      padding: 0.5rem 0.7rem;
      background: var(--surface-highest);
      border-radius: var(--radius-md);
      font-family: 'JetBrains Mono', monospace;
      font-size: 0.75rem;
      color: var(--primary);
      font-weight: 500;
    }

    .why-btn {
      display: inline-flex;
      align-items: center;
      gap: 0.3rem;
      background: none;
      border: 1.5px solid var(--outline-variant);
      color: var(--outline);
      font-family: 'Inter', sans-serif;
      font-size: 0.7rem;
      font-weight: 600;
      padding: 0.3rem 0.6rem;
      border-radius: var(--radius-full);
      cursor: pointer;
      margin-top: 0.5rem;
      transition: all var(--dur-fast);
    }

    .why-btn:hover {
      border-color: var(--primary);
      color: var(--primary);
    }

    .why-body {
      margin-top: 0.5rem;
      padding: 0.6rem;
      background: rgba(0, 91, 191, 0.06);
      border-radius: var(--radius-md);
      font-size: 0.73rem;
      color: var(--on-surface-variant);
      line-height: 1.5;
      display: none;
    }

    .why-body.open {
      display: block;
    }

    /* Stack */
    .stack-container {
      background: var(--surface-lowest);
      border-radius: var(--radius-xl);
      padding: 0.8rem;
      box-shadow: var(--ambient-shadow);
      min-height: 120px;
    }

    .stack-top-label {
      font-size: 0.62rem;
      font-weight: 700;
      letter-spacing: 0.1em;
      text-transform: uppercase;
      color: var(--primary);
      margin-bottom: 0.5rem;
      display: flex;
      align-items: center;
      gap: 0.4rem;
    }

    .stack-top-label::after {
      content: '';
      flex: 1;
      height: 1px;
      background: var(--outline-variant);
      opacity: 0.4;
    }

    .stack-items {
      display: flex;
      flex-direction: column-reverse;
      gap: 0.3rem;
    }

    .stack-item {
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 0.45rem 0.7rem;
      background: var(--surface-highest);
      border-radius: var(--radius-md);
      font-family: 'JetBrains Mono', monospace;
      font-size: 0.73rem;
      color: var(--primary);
      font-weight: 600;
      animation: slideUpIn var(--dur-fast) var(--ease-socialite);
    }

    .stack-item .si-label {
      color: var(--outline);
      font-size: 0.62rem;
      font-family: 'Inter', sans-serif;
    }

    @keyframes slideUpIn {
      from {
        opacity: 0;
        transform: translateY(6px);
      }

      to {
        opacity: 1;
        transform: translateY(0);
      }
    }

    /* Tables tab */
    .data-table-wrap {
      background: var(--surface-lowest);
      border-radius: var(--radius-xl);
      overflow: hidden;
      box-shadow: var(--ambient-shadow);
      margin-bottom: 0.75rem;
    }

    .dt-header {
      padding: 0.6rem 0.8rem;
      background: var(--surface-high);
      font-size: 0.65rem;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.1em;
      color: var(--primary);
      display: flex;
      align-items: center;
      justify-content: space-between;
    }

    .data-table {
      width: 100%;
      border-collapse: collapse;
      font-size: 0.72rem;
      font-family: 'JetBrains Mono', monospace;
    }

    .data-table th {
      background: var(--surface-highest);
      color: var(--outline);
      font-size: 0.63rem;
      font-weight: 700;
      letter-spacing: 0.06em;
      text-transform: uppercase;
      padding: 0.4rem 0.6rem;
      text-align: left;
    }

    .data-table td {
      padding: 0.38rem 0.6rem;
      color: var(--on-surface-variant);
    }

    .data-table tr:hover td {
      background: var(--surface-highest);
    }

    .data-table tr.final-r td {
      color: var(--tertiary);
      font-weight: 600;
    }

    /* Simulate tab */
    .sim-section {
      display: flex;
      flex-direction: column;
      gap: 0.6rem;
    }

    .sim-btn {
      width: 100%;
      padding: 0.65rem;
      border-radius: var(--radius-lg);
      border: none;
      font-family: 'Inter', sans-serif;
      font-size: 0.8rem;
      font-weight: 700;
      cursor: pointer;
      transition: all var(--dur-fast) var(--ease-socialite);
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 0.4rem;
    }

    .sim-btn.forward {
      background: linear-gradient(135deg, var(--primary), var(--primary-container));
      color: var(--on-primary);
      box-shadow: 0 4px 12px rgba(0, 91, 191, 0.2);
    }

    .sim-btn.forward:hover {
      transform: translateY(-1px);
      box-shadow: 0 6px 18px rgba(0, 91, 191, 0.3);
    }

    .sim-btn.reverse {
      background: var(--surface-lowest);
      color: var(--primary);
      border: 1.5px solid rgba(0, 91, 191, 0.25);
      box-shadow: var(--lift-shadow);
    }

    .sim-btn.reverse:hover {
      background: rgba(0, 91, 191, 0.06);
    }

    .quick-test-row {
      display: flex;
      gap: 0.4rem;
    }

    .quick-test-input {
      flex: 1;
      background: var(--surface-highest);
      border: none;
      border-bottom: 1.5px solid var(--outline-variant);
      border-radius: var(--radius-md) var(--radius-md) 0 0;
      padding: 0.45rem 0.6rem;
      font-family: 'JetBrains Mono', monospace;
      font-size: 0.82rem;
      color: var(--on-surface);
      outline: none;
      transition: border-color var(--dur-fast);
    }

    .quick-test-input:focus {
      border-bottom-color: var(--primary);
    }

    .quick-test-run {
      padding: 0.45rem 0.8rem;
      background: var(--primary);
      color: var(--on-primary);
      border: none;
      border-radius: var(--radius-md);
      font-family: 'Inter', sans-serif;
      font-size: 0.75rem;
      font-weight: 700;
      cursor: pointer;
      transition: all var(--dur-fast);
    }

    .quick-test-run:hover {
      background: #004ea3;
    }

    .quick-result {
      padding: 0.5rem 0.7rem;
      border-radius: var(--radius-md);
      font-size: 0.78rem;
      font-weight: 600;
      display: none;
    }

    .quick-result.accepted {
      background: rgba(0, 110, 28, 0.1);
      color: var(--secondary);
      display: block;
    }

    .quick-result.rejected {
      background: rgba(187, 22, 19, 0.08);
      color: var(--tertiary);
      display: block;
    }

    /* Theory tab */
    .concept-item {
      background: var(--surface-lowest);
      border-radius: var(--radius-xl);
      padding: 0.7rem 0.9rem;
      margin-bottom: 0.5rem;
      cursor: pointer;
      box-shadow: var(--ambient-shadow);
      transition: box-shadow var(--dur-fast);
    }

    .concept-item:hover {
      box-shadow: var(--lift-shadow);
    }

    .concept-title {
      font-family: 'Manrope', sans-serif;
      font-size: 0.82rem;
      font-weight: 700;
      color: var(--on-surface);
      margin-bottom: 0.2rem;
    }

    .concept-def {
      font-size: 0.73rem;
      color: var(--on-surface-variant);
      line-height: 1.45;
      display: none;
      margin-top: 0.4rem;
    }

    .concept-def.open {
      display: block;
    }

    /* ── Simulation Modal ── */