Rounded outlines, disclosure widgets, and a border reset fix

Three fixes for everyday interface pieces, each checked pixel for pixel against the reference browser. First, outlined controls with no fill now round their corners. A bordered box with rounded corners but no background colour, like a ghost or outline button or a bordered card with a transparent fill, used to square off its corners because the rounding only worked when a background filled the middle. It now draws a proper rounded border ring, so ghost buttons and outlined cards look right. Second, expandable sections work: a details and summary disclosure, the pattern behind FAQs and collapsible panels, now shows its triangle marker, pointing down when open and right when closed, in a proper indent. Third, a common reset is fixed: writing border set to zero now actually removes the border. It was being misread, leaving a stray black border at the inherited thickness, which affected any page that zeroes a border the short way instead of writing border none.