Prevent overscroll bounce for stage and inspector surfaces

[himanshupathak95]

What?

Closes #78564

What?

Adds overscroll-behavior-y: none to .boot-layout__stage and .boot-layout__inspector to prevent the elastic rubber-band effect when scrolling past page boundaries.

Why?

Scrolling past the top or bottom of the stage/inspector surfaces triggers a native elastic bounce. Because these elements use rounded corners (border-radius: 8px), the bounce visually pulls the content away from the rounded edges, exposing the background color underneath. This creates a jarring visual glitch that breaks the polished canvas appearance.

How?

A single CSS property addition

overscroll-behavior-y: none

Non-supporting browsers simply ignore the property.

Testing Instructions

1. Open a macOS machine (Safari or Chrome)
2. Navigate to Settings → Connectors (or any boot-layout settings page)
3. Scroll aggressively past the top and bottom boundaries
4. Verify: no elastic bounce / rubber-band effect occurs on the rounded canvas

Screenshots or screencast

Before

Screen.Recording.2026-05-22.at.22.19.35.mov

After

Screen.Recording.2026-05-22.at.22.18.57.mov

[github-actions]

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Co-authored-by: himanshupathak95 <abcd95@git.wordpress.org>
Co-authored-by: maximebj <maximebj@git.wordpress.org>

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[himanshupathak95]

This matches the approach taken here -

gutenberg/packages/interface/src/components/interface-skeleton/style.scss

Lines 67 to 73 in 082c85a

	// In future versions of Mobile Safari, hopefully overscroll-behavior will be supported.
	// This allows us to disallow the scroll-chaining and rubber-banding that is currently
	// is the cause of the issue outlined above.
	// In other words, the following behavior doesn't yet work in Safari, but if/when
	// it is added, it should take care of the issue.
	// See also: https://drafts.csswg.org/css-overscroll/
	overscroll-behavior-y: none;