:root {
    --bg: #0c0c0c;
    --bg-editor: #0a0a0a;
    --bg-output: #080808;
    --bg-toolbar: #111;
    --border: #1e1e1e;
    --border-focus: #333;
    --gold: #c8a855;
    --gold-dim: rgba(200, 168, 85, 0.5);
    --gold-glow: rgba(200, 168, 85, 0.08);
    --text: #a09888;
    --text-bright: #d8d0c0;
    --text-dim: #5a5448;
    --error: #c85555;
    --error-bg: rgba(200, 85, 85, 0.06);
    --success: #6a9955;
    --mono: 'JetBrains Mono', monospace;
    --serif: 'Cormorant', Georgia, serif;
  }

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

  body {
    background: var(--bg);
    color: var(--text);
    font-family: var(--mono);
    font-size: 14px;
    height: 100vh;
    display: flex;
    flex-direction: column;
    overflow: hidden;
  }

  /* ── Header ── */
  header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 1.25rem;
    height: 48px;
    border-bottom: 1px solid var(--border);
    background: var(--bg);
    flex-shrink: 0;
  }

  .logo {
    font-family: var(--serif);
    font-size: 1.4rem;
    font-weight: 300;
    letter-spacing: 0.06em;
    color: var(--text-bright);
  }

  .header-right {
    display: flex;
    align-items: center;
    gap: 1rem;
  }

  .version-badge {
    font-size: 0.7rem;
    color: var(--text-dim);
    border: 1px solid var(--border);
    padding: 0.2rem 0.5rem;
    border-radius: 3px;
  }

  .header-link {
    font-size: 0.75rem;
    color: var(--text-dim);
    text-decoration: none;
    transition: color 0.15s;
  }
  .header-link:hover { color: var(--gold); }

  /* ── Main layout ── */
  main {
    flex: 1;
    display: grid;
    grid-template-columns: 200px 55fr 45fr;
    min-height: 0;
  }

  /* ── Sidebar ── */
  .sidebar {
    background: var(--bg);
    border-right: 1px solid var(--border);
    display: flex;
    flex-direction: column;
    min-height: 0;
  }
  .sidebar-header {
    display: flex;
    align-items: center;
    padding: 0 0.75rem;
    height: 36px;
    border-bottom: 1px solid var(--border);
    background: var(--bg-toolbar);
    flex-shrink: 0;
  }
  .sidebar-title {
    font-size: 0.7rem;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--text-dim);
  }
  .sidebar-tree {
    flex: 1;
    overflow-y: auto;
    padding: 0.5rem 0;
    scrollbar-width: thin;
    scrollbar-color: var(--border) transparent;
  }
  .tree-category {
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 0.35rem;
    padding: 0.3rem 0.75rem;
    font-size: 0.65rem;
    letter-spacing: 0.06em;
    text-transform: uppercase;
    color: var(--text-dim);
    user-select: none;
  }
  .tree-category:hover { color: var(--text); }
  .tree-chevron {
    font-size: 0.6rem;
    width: 0.8rem;
    text-align: center;
  }
  .tree-items.collapsed { display: none; }
  .tree-file {
    display: block;
    width: 100%;
    padding: 0.25rem 0.75rem 0.25rem 1.8rem;
    font-family: var(--mono);
    font-size: 0.7rem;
    color: var(--text);
    background: none;
    border: none;
    text-align: left;
    cursor: pointer;
    transition: color 0.1s, background 0.1s;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
  }
  .tree-file:hover { color: var(--text-bright); background: var(--gold-glow); }
  .tree-file.active { color: var(--gold); background: var(--gold-glow); }

  /* ── Editor pane ── */
  .pane {
    display: flex;
    flex-direction: column;
    min-height: 0;
    min-width: 0;
  }

  .pane-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 1rem;
    height: 36px;
    border-bottom: 1px solid var(--border);
    background: var(--bg-toolbar);
    flex-shrink: 0;
  }

  .pane-title {
    font-size: 0.7rem;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--text-dim);
  }

  .editor-pane { border-right: 1px solid var(--border); }

  .editor-wrap {
    flex: 1;
    position: relative;
    overflow: hidden;
    min-height: 0;
  }
  .editor-highlight,
  textarea#editor {
    position: absolute;
    top: 0; left: 0;
    width: 100%;
    height: 100%;
    padding: 1.25rem;
    font-family: var(--mono);
    font-size: 13px;
    line-height: 1.65;
    tab-size: 2;
    white-space: pre-wrap;
    word-wrap: break-word;
    overflow-wrap: break-word;
    border: none;
    margin: 0;
  }
  .editor-highlight {
    pointer-events: none;
    color: var(--text-bright);
    background: var(--bg-editor);
    z-index: 0;
    overflow: auto;
    scrollbar-width: thin;
    scrollbar-color: var(--border) transparent;
  }
  textarea#editor {
    color: transparent;
    caret-color: var(--gold);
    background: transparent;
    outline: none;
    resize: none;
    z-index: 1;
    -webkit-text-fill-color: transparent;
    scrollbar-width: thin;
    scrollbar-color: var(--border) transparent;
  }
  textarea#editor::placeholder { color: var(--text-dim); -webkit-text-fill-color: var(--text-dim); }
  textarea#editor::selection { background: var(--gold); color: var(--bg); -webkit-text-fill-color: var(--bg); }
  .editor-highlight.focused { background: #0b0b0b; }
  .hl-comment { color: var(--text-dim); font-style: italic; }
  .hl-string { color: #a8c47a; }
  .hl-keyword { color: var(--gold); }
  .hl-number { color: #d19a66; }
  .hl-boolean { color: #d19a66; }
  .hl-keyword-lit { color: #7aacb8; }
  .hl-paren { color: #6a6258; }

  /* ── Run button ── */
  .run-btn {
    font-family: var(--mono);
    font-size: 0.7rem;
    letter-spacing: 0.05em;
    color: var(--bg);
    background: var(--gold);
    border: none;
    padding: 0.3rem 0.9rem;
    border-radius: 3px;
    cursor: pointer;
    transition: opacity 0.15s;
  }
  .run-btn:hover { opacity: 0.85; }
  .run-btn:active { opacity: 0.7; }
  .run-btn:disabled {
    opacity: 0.4;
    cursor: not-allowed;
  }

  .run-btn .shortcut {
    opacity: 0.6;
    margin-left: 0.4rem;
  }

  /* ── Engine toggle ── */
  .engine-toggle {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-size: 0.65rem;
    color: var(--text-dim);
    letter-spacing: 0.04em;
  }
  .engine-toggle label {
    cursor: pointer;
    padding: 0.2rem 0.45rem;
    border-radius: 3px;
    transition: color 0.15s, background 0.15s;
  }
  .engine-toggle label:hover { color: var(--text); }
  .engine-toggle label.active {
    color: var(--gold);
    background: var(--gold-glow);
  }
  .engine-toggle input[type="radio"] { display: none; }

  /* ── Output pane ── */
  #output {
    flex: 1;
    overflow-y: auto;
    padding: 1.25rem;
    background: var(--bg-output);
    font-family: var(--mono);
    font-size: 13px;
    line-height: 1.65;
    scrollbar-width: thin;
    scrollbar-color: var(--border) transparent;
  }

  .output-line { color: var(--text); white-space: pre; }
  .output-value {
    color: var(--gold);
    border-left: 2px solid var(--gold-dim);
    padding-left: 0.75rem;
    margin-top: 0.25rem;
    white-space: pre;
  }
  .output-error {
    color: var(--error);
    background: var(--error-bg);
    padding: 0.5rem 0.75rem;
    border-radius: 4px;
    border-left: 2px solid var(--error);
    white-space: pre-wrap;
  }
  .output-timing {
    color: var(--text-dim);
    font-size: 0.7rem;
    margin-top: 0.75rem;
    padding-top: 0.5rem;
    border-top: 1px solid var(--border);
  }
  .output-welcome {
    color: var(--text-dim);
    font-style: italic;
  }

  /* ── Status bar ── */
  .status-bar {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 1rem;
    height: 24px;
    border-top: 1px solid var(--border);
    background: var(--bg);
    flex-shrink: 0;
  }

  .status-text {
    font-size: 0.65rem;
    color: var(--text-dim);
  }

  .status-ready { color: var(--success); }
  .status-loading { color: var(--gold); }
  .status-error { color: var(--error); }

  /* ── Loading overlay ── */
  .loading-overlay {
    position: fixed;
    inset: 0;
    background: var(--bg);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    z-index: 100;
    transition: opacity 0.4s;
  }
  .loading-overlay.hidden {
    opacity: 0;
    pointer-events: none;
  }
  .loading-title {
    font-family: var(--serif);
    font-size: 2.5rem;
    font-weight: 300;
    letter-spacing: 0.06em;
    color: var(--text-bright);
    margin-bottom: 1.5rem;
  }
  .loading-dots {
    display: flex;
    gap: 0.4rem;
  }
  .loading-dots span {
    width: 6px;
    height: 6px;
    background: var(--gold);
    border-radius: 50%;
    animation: pulse 1.2s infinite;
  }
  .loading-dots span:nth-child(2) { animation-delay: 0.2s; }
  .loading-dots span:nth-child(3) { animation-delay: 0.4s; }
  @keyframes pulse {
    0%, 100% { opacity: 0.2; }
    50% { opacity: 1; }
  }

  /* ── Responsive ── */
  @media (max-width: 768px) {
    main { grid-template-columns: 1fr; grid-template-rows: auto 1fr 1fr; }
    .sidebar { max-height: 200px; border-right: none; border-bottom: 1px solid var(--border); }
    .editor-pane { border-right: none; border-bottom: 1px solid var(--border); }
  }