Safari: fix scrollbar overlay issue

[naltatis]

Refs #28566

Working around a Safari bug where inline scrollbars are not drawn in layer order.

[sourcery-ai]

Hey - I've left some high level feedback:

• Hiding the scrollbar with opacity: 0 may hurt discoverability and accessibility for keyboard/mouse users; consider a workaround that preserves a visible scrollbar (e.g., adjusting z-index stacking with an inner wrapper or using position/pointer-events) instead of fully hiding it.
• If this rule is intended to target only Safari’s behavior, consider wrapping it in a WebKit-specific @supports or adding a more explicit browser-guarding approach so other browsers don’t inherit the scrollbar hiding unnecessarily.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Hiding the scrollbar with `opacity: 0` may hurt discoverability and accessibility for keyboard/mouse users; consider a workaround that preserves a visible scrollbar (e.g., adjusting z-index stacking with an inner wrapper or using `position`/`pointer-events`) instead of fully hiding it.
- If this rule is intended to target only Safari’s behavior, consider wrapping it in a WebKit-specific `@supports` or adding a more explicit browser-guarding approach so other browsers don’t inherit the scrollbar hiding unnecessarily.

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