Block editor: unwanted scroll bar while loading.

[matiasbenedetto]

Description

On load time the block editor displays an unwanted scroll bar. Please take a look at the screenshot below.

I'm tagging this issue with zoom-out tag because this seems to be the result of the changes introduced in #67126

Specifically this line:

gutenberg/packages/block-editor/src/components/iframe/content.scss

Lines 22 to 24 in 857ca64

	// Force preserving a scrollbar gutter as scrollbar-gutter isn't supported in all browsers yet,
	// and removing the scrollbar causes the content to shift.
	overflow-y: scroll;

Step-by-step reproduction instructions

1. Use Gutenberg trunk and TT5 theme.
2. Browse theme style variations in the sidebar.
3. Observe the unwanted scroll bars while the block editors are loading

Screenshots, screen recording, code snippet

Environment info

• WordPress 6.7.1
• Gutenberg trunk

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure

[t-hamano]

I'm wondering why the theme style preview or palette preview even needs zoom-out related CSS class names or variables 🤔

cc @jeryj @draganescu @ajlende

[jeryj]

I think this should be fixed by #67495 and #67496

Ah, never mind. I think this is due to the animation assuming the resulting canvas will have a scrollbar. If the height of the content is less than the frame, we won't want to force a scrollbar.