fix(docs): dialog navbar issues

[chakrihacker]

Description

Hides the navbar signup/login buttons (#adu-root) when a Universal Components dialog is open. When a UC dialog opens, it overlaps the top navigation area, causing the navbar CTA buttons to render on top of or beneath the dialog in a visually broken state. This fix uses a CSS body:has() parent selector to detect an open dialog and fade out #adu-root with a short opacity transition, then defers visibility: hidden until after the fade completes so the buttons are removed from tab order cleanly.

References

Testing

1. Open any page in the docs site that renders a Universal Components dialog (e.g. Member Management).
2. Trigger the dialog to open — confirm the navbar CTA buttons fade out and are no longer visible or focusable.
3. Close the dialog — confirm the buttons fade back in.
4. Verify no layout shift or z-index conflicts on light and dark mode.

Checklist

• I've read and followed CONTRIBUTING.md.
• I've tested the site build for this change locally.
• I've made appropriate docs updates for any code or config changes.
• I've coordinated with the Product Docs and/or Docs Management team about non-trivial changes.

[grandmaester]

@chakrihacker Can we check if this working fine else where?

[chakrihacker]

This doesn't affect at other places