details / summary have minor animation of collapse oddness on mobile / multiline input

[btopro]

Minor. But multi-line text for a summary tag will duplicate the collapse toggle 'icon' area off to the right. probably an issue of a bg image needing to not repeat

Also w/ the new demo content in page-section if you are on mobile and expand then collapse content, about 1 second after collapse it lurches forward an additional 4px or so