:root {
      --md-width: 720px;
    }

    * {
      box-sizing: border-box;
    }

    html, body {
      margin: 0;
      padding: 0;
      height: 100%;
      background: var(--bg-app);
      color: var(--text-body);
      font-family: var(--font-ui);
      font-size: var(--font-size-base);
      -webkit-font-smoothing: antialiased;
      text-rendering: optimizeLegibility;
      overflow: hidden;
    }

    /* Thin Custom Scrollbars */
    ::-webkit-scrollbar {
      width: 10px;
      height: 10px;
    }
    ::-webkit-scrollbar-track {
      background: transparent;
    }
    ::-webkit-scrollbar-thumb {
      background: var(--border-button);
      border-radius: 5px;
      border: 2px solid transparent;
      background-clip: padding-box;
    }
    ::-webkit-scrollbar-thumb:hover {
      background: var(--text-muted);
      background-clip: padding-box;
    }

    /* App Layout */
    #app {
      display: flex;
      flex-direction: column;
      height: 100vh;
      width: 100vw;
      overflow: hidden;
    }

    /* Top Chrome / Tabstrip */
    .tabstrip {
      display: flex;
      align-items: stretch;
      height: 42px;
      background: var(--bg-tabstrip);
      border-bottom: 1px solid var(--border);
      flex: none;
      user-select: none;
    }

    .tab {
      display: flex;
      align-items: center;
      gap: 8px;
      padding: 0 16px;
      background: var(--bg-app);
      border-right: 1px solid var(--border);
      border-top: 2px solid var(--accent);
      font-size: 12px;
      color: var(--text-primary);
      font-family: var(--font-ui);
    }

    .tab-dot {
      color: var(--accent);
      font-size: 8px;
    }

    .toolbar-actions {
      margin-left: auto;
      display: flex;
      align-items: center;
      gap: 8px;
      padding: 0 12px;
    }

    .mode-switch {
      display: flex;
      background: var(--bg-raised);
      border-radius: var(--radius-large);
      padding: 2px;
      gap: 2px;
    }

    .mode-pill {
      padding: 4px 14px;
      border-radius: var(--radius-medium);
      font-size: 11px;
      font-family: var(--font-ui);
    }

    .mode-pill.active {
      background: var(--accent);
      color: var(--accent-fg);
      font-weight: 600;
    }

    .mode-pill.inactive {
      color: var(--text-secondary);
      background: transparent;
    }

    .tool-btn {
      padding: 5px 12px;
      border: 1px solid var(--border-button);
      border-radius: var(--radius-large);
      font-size: 11px;
      color: var(--text-button);
      background: var(--btn-bg);
      cursor: pointer;
      font-family: var(--font-ui);
      display: inline-flex;
      align-items: center;
      gap: 4px;
      transition: all 0.15s ease;
    }
    .tool-btn:hover {
      border-color: var(--accent);
      color: var(--text-primary);
    }

    .theme-toggle {
      width: 28px;
      height: 28px;
      border-radius: var(--radius-large);
      border: 1px solid var(--border-button);
      display: grid;
      place-items: center;
      color: var(--text-secondary);
      font-size: 13px;
      background: var(--btn-bg);
      cursor: pointer;
      transition: all 0.15s ease;
    }
    .theme-toggle:hover {
      border-color: var(--accent);
      color: var(--text-primary);
    }

    /* Main Workspace */
    .workspace {
      display: flex;
      flex: 1;
      min-height: 0;
      background: var(--bg-app);
    }

    /* Sidebar Outline */
    .sidebar {
      width: 250px;
      flex: none;
      background: var(--bg-sidebar);
      border-right: 1px solid var(--border);
      display: flex;
      flex-direction: column;
      overflow-y: auto;
      user-select: none;
    }

    @media (max-width: 960px) {
      .sidebar {
        display: none;
      }
    }

    .sidebar-section-title {
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 14px 16px 8px;
      font-size: 10px;
      letter-spacing: 0.08em;
      color: var(--text-muted);
      font-weight: 600;
    }

    .outline-list {
      display: flex;
      flex-direction: column;
      gap: 2px;
      padding: 0 8px 16px;
    }

    .outline-empty {
      padding: 8px 10px;
      font-size: 11px;
      color: var(--text-muted);
      font-style: italic;
    }

    .outline-link {
      display: block;
      padding: 6px 10px;
      border-radius: var(--radius-medium);
      color: var(--text-secondary);
      font-size: 11.5px;
      line-height: 1.4;
      text-decoration: none;
      font-family: var(--font-ui);
      white-space: nowrap;
      overflow: hidden;
      text-overflow: ellipsis;
      transition: background 0.12s, color 0.12s;
    }
    .outline-link:hover {
      background: var(--bg-hover);
      color: var(--text-primary);
    }
    .outline-link.active {
      background: var(--active-row-bg);
      color: var(--accent);
      font-weight: 600;
    }

    /* Preview Scroller */
    .preview-scroll {
      flex: 1;
      overflow-y: auto;
      display: flex;
      justify-content: center;
      min-height: 0;
      contain: layout style;
      scroll-behavior: smooth;
    }

    /* Prose Area */
    .prose {
      width: var(--md-width, 720px);
      max-width: 100%;
      padding: 44px 24px 96px;
      font-family: var(--font-prose);
      font-size: 15px;
      line-height: 1.7;
      color: var(--text-body);
      cursor: text;
      user-select: text;
      -webkit-user-select: text;
    }

    .prose ::selection {
      background: var(--selection-bg);
    }

    /* Headings */
    .prose h1 {
      font-size: 32px;
      font-weight: 600;
      letter-spacing: -0.02em;
      color: var(--text-primary);
      padding-bottom: 12px;
      border-bottom: 1px solid var(--border);
      margin: 0 0 18px;
    }

    .prose h2 {
      font-size: 21px;
      font-weight: 600;
      color: var(--text-primary);
      margin: 32px 0 12px;
      scroll-margin-top: 16px;
    }

    .prose h3 {
      font-size: 17px;
      font-weight: 600;
      color: var(--text-primary);
      margin: 22px 0 10px;
      scroll-margin-top: 16px;
    }

    .prose h4,
    .prose h5,
    .prose h6 {
      font-size: 15px;
      font-weight: 600;
      color: var(--text-primary);
      margin: 20px 0 8px;
    }

    /* Paragraphs & Text */
    .prose p {
      margin: 0 0 20px;
    }

    .prose strong {
      color: var(--text-primary);
      font-weight: 600;
    }

    .prose em {
      font-style: italic;
    }

    .prose del {
      color: var(--text-muted);
      text-decoration: line-through;
    }

    .prose a {
      color: var(--accent);
      text-decoration: none;
    }
    .prose a:hover {
      text-decoration: underline;
    }

    .prose blockquote {
      margin: 0 0 20px;
      padding-left: 16px;
      border-left: 2px solid var(--border);
      color: var(--text-secondary);
    }

    .prose hr {
      border: none;
      border-top: 1px solid var(--border);
      margin: 28px 0;
    }

    /* Lists */
    .prose ul,
    .prose ol {
      margin: 0 0 22px;
      padding-left: 22px;
    }

    .prose li {
      margin-bottom: 8px;
    }
    .prose li:last-child {
      margin-bottom: 0;
    }

    /* GFM Checkboxes */
    .prose input[type="checkbox"].task-toggle {
      accent-color: var(--accent);
      vertical-align: -1px;
      margin: 0 6px 0 0;
      cursor: default;
    }

    .prose li:has(> input.task-toggle) {
      list-style: none;
      margin-left: -1.4em;
    }

    /* Inline code chips */
    .prose code {
      font-family: var(--font-mono);
      font-size: 12.5px;
      background: var(--bg-inline-code);
      padding: 2px 6px;
      border-radius: 4px;
      color: var(--code-amber);
    }

    .prose :is(h1, h2, h3, h4, h5, h6) code {
      font: inherit;
      letter-spacing: inherit;
      color: inherit;
      background: none;
      padding: 0;
      border-radius: 0;
    }

    /* Code blocks */
    .prose pre {
      background: var(--code-block-bg);
      border: 1px solid var(--code-block-border);
      border-radius: 8px;
      padding: 14px 18px;
      margin: 0 0 22px;
      overflow-x: auto;
    }

    .prose pre code {
      font-family: var(--font-mono);
      font-size: 13px;
      background: none;
      padding: 0;
      border-radius: 0;
      color: var(--code-block-text);
      line-height: 1.55;
    }

    .prose pre code .sh-prompt {
      color: var(--code-block-prompt);
    }

    /* Tables */
    .prose table {
      border-collapse: collapse;
      width: 100%;
      font-size: 13.5px;
      margin: 0 0 24px;
    }

    .prose th {
      text-align: left;
      padding: 9px 14px;
      border-bottom: 2px solid var(--accent);
      font-weight: 600;
      color: var(--text-primary);
      font-family: var(--font-prose);
    }

    .prose td {
      padding: 9px 14px;
      border-bottom: 1px solid var(--border);
      font-family: var(--font-prose);
    }

    .prose td:first-child {
      font-family: var(--font-mono);
      font-size: 12.5px;
    }

    .prose td:nth-child(2) {
      color: var(--text-secondary);
    }

    /* Images */
    .prose img {
      max-width: 100%;
      height: auto;
      border-radius: 6px;
      display: block;
      margin: 0 0 22px;
    }

    /* Footer / Status bar */
    .statusbar {
      display: flex;
      align-items: center;
      gap: 16px;
      height: 28px;
      padding: 0 14px;
      background: var(--bg-statusbar);
      border-top: 1px solid var(--border);
      flex: none;
      font-size: 10.5px;
      color: var(--text-muted);
      user-select: none;
    }

    .status-saved {
      color: var(--success);
    }

    /* ---- charts (```chart) ---------------------------------------------- */
    figure.h7-chart {
      margin: 22px 0 26px;
      padding: 16px 16px 8px;
      background: var(--bg-raised);
      border: 1px solid var(--border);
      border-radius: var(--radius-medium);
      overflow-x: auto;
    }
    figure.h7-chart .h7-chart-cap {
      font-family: var(--font-mono);
      font-size: 11px;
      letter-spacing: 0.08em;
      text-transform: uppercase;
      color: var(--text-secondary);
      margin: 0 0 12px;
      padding-bottom: 8px;
      border-bottom: 2px solid var(--accent);
    }
    figure.h7-chart .h7-chart-body { min-height: 40px; }
    figure.h7-chart svg { display: block; max-width: 100%; height: auto; }
    figure.h7-chart .h7-chart-error {
      font-family: var(--font-mono);
      font-size: 12px;
      color: var(--danger);
      padding: 12px 0;
    }
    figure.h7-chart .h7-axis text { font-family: var(--font-mono); font-size: 11px; }