see, e.g., https://wpt.fyi/results/css/css-contain?q=%28label%3Ainterop-2022-contain%20or%20label%3Ainterop-2023-contain%29%20is%3Adifferent&run_id=5179945829007360&run_id=5129256222326784&run_id=5105446492307456

e.g. https://wpt.fyi/analyzer?screenshot=sha1%3Aa8193aa1d36a2e7c269c79da3fdfef70d986dd6d&screenshot=sha1%3A1bc22df9e9199ea9890c7d35fbf48b11b87cf11b or https://wpt.fyi/analyzer?screenshot=sha1%3A8d5e20aecf8b5cc808f48b90c8ee7e09f88d3c38&screenshot=sha1%3Abc778655cc0444e393609feb97a0948c43475817

We seem to end up with a transparent grey overlay at the top (the shadow from the tab bar?), one pixel high. What's more odd given that is we also are lacking the rounded corners we'd expect from the window, which extends for more than a single pixel—so we aren't just cropping the screenshot of the window off-by-one-pixel, we have some larger difference here.