The bottom of the Stackoverflow logo is being cut off on stackoverflow.com, the height of its container is one pixel too short.
This is reproducible on Chrome on retina Mac on the non-default zoom level.
Start at default zoom (command 0) and then make the canvas render at 90% (command -) and you will see the rounding error / cropping. Zooming out to 50% doesn't show this cropping in each successive step. Magnifying the page also doesn't seem to have this artifact.
It might be the CSS is fine and the browser is to blame?