Keep collapsed panel arrows horizontal

agent.md

@@ -42,6 +42,7 @@ This project replaces the Excel/VBA workflow named `Catalog maker - 20` with a N
 - Top headers for the sidebar, secondary panel and main workspace must use one shared fixed height so the columns align visually across the application.
 - All top panel headers must use the shared `panel-header` component class, including identical background, border, typography, spacing and dark/light theme behavior. Do not style `Catalog controls`, `Product details` or `Main workspace` headers independently.
 - The three top panel headers must share the same top baseline and visual bounds. The sidebar header must compensate for the sidebar's inner padding so it is not offset from the product-details and main-workspace headers.
+- Collapse/expand arrow buttons must keep `writing-mode: horizontal-tb` when their parent panel uses vertical writing mode, so the arrow glyph remains visually directional.
 - Panel collapse/open controls must use the shared `panel-control-button` style; do not create separate visual variants for `X`, chevrons or future panel toggles.
 - Verify shared panel-control styling through computed browser styles, not only by checking class names.
 - Use Playwright to inspect the rendered result after every visual change at desktop and narrow viewport sizes.

src/tailwind.css

@@ -120,6 +120,8 @@
   .column-toggle { @apply inline-flex h-5 w-5 shrink-0 items-center justify-center rounded border border-slate-400 bg-white text-sm leading-none text-slate-700 shadow-sm transition hover:border-slate-500 hover:bg-slate-200 focus:outline-none focus:ring-2 focus:ring-catalog-focus/25; }
   .secondary-panel .field-grid { @apply overflow-hidden; }
   .secondary-collapsed .secondary-panel .column-header { @apply h-full flex-col justify-start py-1; writing-mode: vertical-rl; }
+  .secondary-collapsed .secondary-panel .column-header .column-toggle,
+  .workspace-collapsed .main-workspace .workspace-header .column-toggle { writing-mode: horizontal-tb; }
   .secondary-collapsed .secondary-panel .field-grid { display: none; }
   .workspace-collapsed .main-workspace .workspace-header { @apply h-full flex-col justify-start py-1; writing-mode: vertical-rl; }
   .workspace-collapsed .main-workspace .workspace-header span,