StyleBook for Classic Theme: Resize is not smooth

[t-hamano]

Description

In classic themes that support editor styles, you will see the Design submenu in the Appearance menu. You can access the StyleBook through that menu.

The StyleBook canvas can be resized by dragging the handles with the mouse, but it is not smooth.

When I checked with the browser's network tool, it seems that a lot of requests are being made every time the canvas is resized. We need to investigate the exact cause, but this might be related.

Step-by-step reproduction instructions

• Enable Twenty Twenty-One theme
• Appearance > Design > Styles
• Resize the Stylebook canvas

Screenshots, screen recording, code snippet

415641591fd9a77ba139ea19f8965cb8.mp4

Environment info

No response

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