The page root Container's default 20px padding framed every AI-built section
in a white margin (visible in every eval screenshot). New AI page/site
replaces now set padding 0 on the page root unless the model set padding
itself. Saved pages, section inserts, patches and the Container default are
unchanged, so existing sites do not move.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>