In the Site Editor nav view (canvas=view), the navigation preview renders top-left aligned — then visually jumps to centered when entering edit mode. This is both hard to read and disorienting.

Root cause: The iframe centering CSS (display:flex; align-items:center; justify-content:center on .block-editor-iframe__html) was gated entirely on enableResizing, which is explicitly disabled in preview/view mode (! isPreview). Centering and resizing were conflated in a single flag.

Change — packages/editor/src/components/visual-editor/index.js:

• Extract isNavigationOrDesignPostType (wp_navigation, wp_template_part, wp_block) from the enableResizing condition
• Apply iframe centering CSS based on isNavigationOrDesignPostType (view and edit modes) rather than enableResizing (edit mode only)
• enableResizing and the min-height:0!important guard on .is-root-container are unchanged — resizing remains edit-mode only

// Before: centering tied to enableResizing (edit mode only)
enableResizing
  ? `.block-editor-iframe__html{...display:flex;align-items:center;...}`
  : ''

// After: centering for design post types regardless of preview mode
isNavigationOrDesignPostType
  ? `.block-editor-iframe__html{...display:flex;align-items:center;...}`
  : ''

The same fix benefits template parts and patterns in their respective view-mode previews, which share the same rendering path.

• Fixes Center Navigation Preview in Site Editor Nav View #75734

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