:root {
      --bg: #1e1e1e;
      --bg-elevated: #252526;
      --bg-sidebar: #181818;
      --bg-header: #2d2d2d;
      --border: #3c3c3c;
      --text: #e8e8e8;
      --text-muted: #9a9a9a;
      --accent: #0e639c;
      --accent-hover: #1177bb;
      --accent-focus: #4fc3f7;
      --success: #4ec9b0;
      --warn: #dcdcaa;
      --error: #f48771;
      --info: #9cdcfe;
      --log: #ce9178;
      --touch-min: 44px;
      --header-h: 48px;
      --tab-h: 44px;
      --bottom-default: 160px;
      --radius: 6px;
      --font-ui: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
      --font-mono: "Cascadia Code", "Fira Code", ui-monospace, Consolas, "Courier New", monospace;
      --safe-top: env(safe-area-inset-top, 0px);
      --safe-bottom: env(safe-area-inset-bottom, 0px);
      --safe-left: env(safe-area-inset-left, 0px);
      --safe-right: env(safe-area-inset-right, 0px);
    }

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

    *, *::before, *::after { box-sizing: border-box; }
    html {
      height: 100%;
      -webkit-text-size-adjust: 100%;
      text-size-adjust: 100%;
    }
    body {
      margin: 0;
      min-height: 100%;
      min-height: 100dvh;
      font-family: var(--font-ui);
      font-size: 16px;
      line-height: 1.5;
      background: var(--bg);
      color: var(--text);
      overflow: hidden;
    }
    button, input, select, textarea { font: inherit; color: inherit; }
    a { color: var(--info); }
    a:focus-visible { outline: 2px solid var(--accent-focus); outline-offset: 2px; }
    code {
      font-family: var(--font-mono);
      font-size: 0.9em;
      background: rgba(255,255,255,0.06);
      padding: 0.1em 0.35em;
      border-radius: 3px;
    }

    .skip-link {
      position: absolute;
      left: -9999px;
      top: 0;
      z-index: 100;
      padding: 0.75rem 1rem;
      background: var(--accent);
      color: #fff;
      text-decoration: none;
      font-weight: 600;
    }
    .skip-link:focus {
      left: var(--safe-left);
      top: var(--safe-top);
    }

    #app {
      display: flex;
      flex-direction: column;
      height: 100dvh;
      height: 100vh;
      max-height: 100dvh;
      padding-top: var(--safe-top);
      padding-bottom: var(--safe-bottom);
      padding-left: var(--safe-left);
      padding-right: var(--safe-right);
    }

    #toolbar {
      display: flex;
      flex-wrap: wrap;
      align-items: center;
      gap: 0.5rem;
      min-height: var(--header-h);
      padding: 0.4rem 0.6rem;
      background: var(--bg-header);
      border-bottom: 1px solid var(--border);
      flex-shrink: 0;
    }
    .btn {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      gap: 0.35rem;
      min-height: var(--touch-min);
      min-width: var(--touch-min);
      padding: 0.4rem 0.85rem;
      border: none;
      border-radius: var(--radius);
      background: var(--accent);
      color: #fff;
      font-size: 0.875rem;
      font-weight: 600;
      cursor: pointer;
      touch-action: manipulation;
      -webkit-tap-highlight-color: transparent;
    }
    .btn:hover { background: var(--accent-hover); }
    .btn:focus-visible {
      outline: 2px solid var(--accent-focus);
      outline-offset: 2px;
    }
    .btn:disabled { opacity: 0.5; cursor: not-allowed; }
    .btn-secondary {
      background: transparent;
      border: 1px solid var(--border);
      color: var(--text);
    }
    .btn-secondary:hover { background: rgba(255,255,255,0.08); }
    .btn-ghost {
      background: transparent;
      color: var(--text-muted);
      border: none;
    }
    .btn-ghost:hover,
    .btn-ghost[aria-expanded="true"] {
      color: var(--text);
      background: rgba(255,255,255,0.08);
    }
    .btn-icon {
      padding: 0;
      width: var(--touch-min);
    }
    .toolbar-group {
      display: flex;
      flex-wrap: wrap;
      align-items: center;
      gap: 0.4rem;
    }
    .toolbar-spacer {
      flex: 1 1 auto;
      min-width: 0.5rem;
    }
    #status {
      font-family: var(--font-mono);
      font-size: 0.75rem;
      color: var(--text-muted);
      white-space: nowrap;
      max-width: 40vw;
      overflow: hidden;
      text-overflow: ellipsis;
    }
    #status[data-state="ok"] { color: var(--success); }
    #status[data-state="err"] { color: var(--error); }

    #workspace {
      flex: 1 1 auto;
      display: flex;
      flex-direction: column;
      min-height: 0;
      position: relative;
    }

    #tab-bar {
      display: flex;
      flex-shrink: 0;
      overflow-x: auto;
      -webkit-overflow-scrolling: touch;
      scrollbar-width: none;
      background: var(--bg-elevated);
      border-bottom: 1px solid var(--border);
      min-height: var(--tab-h);
    }
    #tab-bar::-webkit-scrollbar { display: none; }
    [role="tab"] {
      flex: 1 0 auto;
      min-width: 4.5rem;
      min-height: var(--tab-h);
      padding: 0.5rem 0.75rem;
      border: none;
      border-bottom: 3px solid transparent;
      background: transparent;
      color: var(--text-muted);
      font-size: 0.8125rem;
      font-weight: 600;
      cursor: pointer;
      touch-action: manipulation;
      white-space: nowrap;
    }
    [role="tab"]:hover { color: var(--text); background: rgba(255,255,255,0.04); }
    [role="tab"][aria-selected="true"] {
      color: #fff;
      border-bottom-color: var(--accent);
    }
    [role="tab"]:focus-visible {
      outline: 2px solid var(--accent-focus);
      outline-offset: -2px;
    }

    #panels {
      flex: 1 1 auto;
      display: flex;
      flex-direction: column;
      min-height: 0;
      position: relative;
    }
    .panel {
      display: none;
      flex-direction: column;
      flex: 1 1 auto;
      min-height: 0;
      min-width: 0;
    }
    .panel.is-active { display: flex; }
    .panel-label {
      display: flex;
      align-items: center;
      gap: 0.5rem;
      flex-shrink: 0;
      height: 32px;
      padding: 0 0.75rem;
      font-size: 0.75rem;
      font-weight: 500;
      color: var(--text-muted);
      background: var(--bg-elevated);
      border-bottom: 1px solid var(--border);
    }
    .panel-label .dot {
      width: 8px;
      height: 8px;
      border-radius: 50%;
      flex-shrink: 0;
    }
    .dot-fscss { background: #c586c0; }
    .dot-css { background: #569cd6; }
    .dot-js { background: #dcdcaa; }
    .dot-html { background: #ce9178; }
    .editor-host {
      flex: 1 1 auto;
      min-height: 0;
      width: 100%;
    }
    .editor-host .monaco-editor {
      width: 100% !important;
      height: 100% !important;
    }

    #preview-frame {
      flex: 1 1 auto;
      width: 100%;
      min-height: 0;
      border: none;
      background: #fff;
    }

    #bottom {
      display: flex;
      flex-direction: column;
      flex-shrink: 0;
      height: var(--bottom-default);
      min-height: 100px;
      max-height: 55dvh;
      background: var(--bg);
      border-top: 1px solid var(--border);
    }
    #resize-handle {
      height: 12px;
      flex-shrink: 0;
      cursor: ns-resize;
      touch-action: none;
      background: transparent;
      position: relative;
    }
    #resize-handle::after {
      content: "";
      position: absolute;
      left: 50%;
      top: 50%;
      transform: translate(-50%, -50%);
      width: 40px;
      height: 4px;
      border-radius: 2px;
      background: var(--border);
    }
    #resize-handle:hover::after,
    #resize-handle:focus-visible::after { background: var(--accent); }
    #resize-handle:focus-visible {
      outline: 2px solid var(--accent-focus);
      outline-offset: -2px;
    }
    #bottom-header {
      display: flex;
      align-items: center;
      gap: 0.5rem;
      flex-shrink: 0;
      min-height: 36px;
      padding: 0 0.6rem;
      font-size: 0.75rem;
      font-family: var(--font-mono);
      color: var(--text-muted);
      background: var(--bg-elevated);
      border-bottom: 1px solid var(--border);
    }
    #bottom-header .prompt { color: var(--success); }
    #logs {
      flex: 1 1 auto;
      overflow: auto;
      -webkit-overflow-scrolling: touch;
      padding: 0.5rem 0.75rem;
      font-family: var(--font-mono);
      font-size: 0.75rem;
      line-height: 1.55;
      white-space: pre-wrap;
      word-break: break-word;
    }
    .log-line { margin: 0 0 0.15rem; }
    .log-line .ts { color: var(--text-muted); margin-right: 0.5rem; }
    .log-line[data-level="log"] .lvl { color: var(--log); }
    .log-line[data-level="warn"] .lvl { color: var(--warn); }
    .log-line[data-level="info"] .lvl { color: var(--info); }
    .log-line[data-level="error"] .lvl { color: var(--error); }
    .log-line[data-level="system"] .lvl { color: var(--success); }
    .log-empty {
      color: var(--text-muted);
      font-style: italic;
      padding: 0.5rem 0;
    }

    #sidebar-backdrop {
      display: none;
      position: fixed;
      inset: 0;
      z-index: 40;
      background: rgba(0, 0, 0, 0.55);
      border: none;
      padding: 0;
      cursor: pointer;
    }
    #sidebar-backdrop.is-open { display: block; }

    #sidebar {
      position: fixed;
      top: 0;
      left: 0;
      z-index: 50;
      width: min(300px, 88vw);
      height: 100%;
      height: 100dvh;
      background: var(--bg-sidebar);
      border-right: 1px solid var(--border);
      transform: translateX(-105%);
      transition: transform 0.2s ease;
      display: flex;
      flex-direction: column;
      overflow: hidden;
      padding-top: var(--safe-top);
      padding-bottom: var(--safe-bottom);
    }
    #sidebar.is-open {
      transform: translateX(0);
      box-shadow: 4px 0 24px rgba(0, 0, 0, 0.45);
    }
    .sidebar-header {
      display: flex;
      align-items: center;
      justify-content: space-between;
      gap: 0.5rem;
      min-height: var(--header-h);
      padding: 0 0.75rem;
      border-bottom: 1px solid var(--border);
      flex-shrink: 0;
    }
    .sidebar-header h1 {
      margin: 0;
      font-size: 0.9375rem;
      font-weight: 700;
    }
    .sidebar-body {
      flex: 1 1 auto;
      overflow-y: auto;
      -webkit-overflow-scrolling: touch;
    }
    .sidebar-section {
      padding: 0.75rem 0;
      border-bottom: 1px solid var(--border);
    }
    .sidebar-section-title {
      margin: 0 0 0.35rem;
      padding: 0 0.9rem;
      font-size: 0.6875rem;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.06em;
      color: var(--text-muted);
    }
    .nav-item {
      display: flex;
      align-items: center;
      gap: 0.5rem;
      width: 100%;
      min-height: var(--touch-min);
      padding: 0.4rem 0.9rem;
      border: none;
      background: transparent;
      color: var(--text);
      font-size: 0.875rem;
      text-align: left;
      cursor: pointer;
      touch-action: manipulation;
    }
    .nav-item:hover { background: rgba(255,255,255,0.06); }
    .nav-item:focus-visible {
      outline: 2px solid var(--accent-focus);
      outline-offset: -2px;
    }
    .nav-item[aria-current="true"] {
      background: rgba(14, 99, 156, 0.4);
      color: #fff;
    }
    .nav-item .icon { width: 1.25rem; text-align: center; opacity: 0.85; flex-shrink: 0; }
    .lib-hint {
      padding: 0.5rem 0.9rem 0.75rem;
      font-size: 0.75rem;
      color: var(--text-muted);
      line-height: 1.45;
    }
    .sidebar-footer {
      flex-shrink: 0;
      padding: 0.75rem 0.9rem;
      font-size: 0.75rem;
      color: var(--text-muted);
      line-height: 1.5;
      border-top: 1px solid var(--border);
    }

    /* Tablet+ : side-by-side panels */
    @media (min-width: 768px) {
      #panels { flex-direction: row; }
      .panel {
        display: flex;
        flex: 1 1 0;
        border-right: 1px solid var(--border);
        min-width: 0;
      }
      .panel:last-child { border-right: none; }
      .panel.is-hidden-desktop { display: none !important; }
      #bottom { height: 180px; }
    }

    @media (max-height: 420px) {
      #bottom { height: 100px; min-height: 72px; }
      #toolbar { min-height: 40px; }
      .btn { min-height: 36px; min-width: 36px; padding: 0.25rem 0.6rem; }
    }

    @media (forced-colors: active) {
      .btn { border: 1px solid ButtonText; }
      [role="tab"][aria-selected="true"] { border-bottom-color: Highlight; }
      }