The details pill drew its own 1px border with a 10px radius inside .float, which draws the real border at 20px radius and clips with overflow:hidden. The parent's looser curve clipped the pill's tighter corner curve, making the border appear thinner/cut at the corners, in both collapsed and expanded states. Drop the pill's own border/radius so .float is the single border surface, matching the other pills on the page. Ref #222