[fix] Correct WhatsNew popup arrow alignment with help center icon (#5137)

* [fix] Correct WhatsNew popup arrow alignment with help center icon

The arrow positioning was not accounting for additional sidebar icons (terminal and shortcuts)
that were added below the help center icon, causing misalignment. Updated the calculation to
properly position the arrow relative to the help center icon's current location.

Fixes #5126

* [fix] Update small sidebar arrow positioning and improve center alignment

- Fixed small sidebar rule to use consistent calculation with normal sidebar
- Updated positioning to use half icon height for better center alignment
- Both normal and small sidebar now use dynamic CSS variable calculations

Addresses feedback from review by viva-jinyi on CSS specificity and positioning accuracy.

* [fix] Make sidebar CSS variables global for teleported components

- Move --sidebar-width CSS variable to :root to make it accessible globally
- This allows teleported components like WhatsNewPopup to reference sidebar dimensions
- Adjust arrow positioning calculations for better alignment with help center icon
- Add explanatory comments about why these variables need to be global

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* fix: icon-size should be variable

---------

Co-authored-by: Jin Yi <jin12cc@gmail.com>
Co-authored-by: Claude <noreply@anthropic.com>

src/components/sidebar/SideToolbar.vue

@@ -76,6 +76,22 @@ const getTabTooltipSuffix = (tab: SidebarTabExtension) => {
 }
 </script>
 
+<style>
+/* Global CSS variables for sidebar
+ * These variables need to be global (not scoped) because they are used by
+ * teleported components like WhatsNewPopup that render outside the sidebar
+ * but need to reference sidebar dimensions for proper positioning.
+ */
+:root {
+  --sidebar-width: 4rem;
+  --sidebar-icon-size: 1rem;
+}
+
+:root:has(.side-tool-bar-container.small-sidebar) {
+  --sidebar-width: 2.5rem;
+}
+</style>
+
 <style scoped>
 .side-tool-bar-container {
   display: flex;
@@ -88,9 +104,6 @@ const getTabTooltipSuffix = (tab: SidebarTabExtension) => {
   background-color: var(--comfy-menu-secondary-bg);
   color: var(--fg-color);
   box-shadow: var(--bar-shadow);
-
-  --sidebar-width: 4rem;
-  --sidebar-icon-size: 1rem;
 }
 
 .side-tool-bar-container.small-sidebar {