For the first one, no. While CSS can act a little
strangely sometimes, the situation you see here is not one
that would be caused by quirks in the way different browsers handle CSS. For the second one, yes. Different device pixel ratios can
definitely change the size of content on the page,
if you don’t handle it correctly. For the third one, nope. Initial scale isn’t going to cause the
inconsistent zooming that you see here. And for the fourth one, yeah. This could be a reason. Without defining the viewport,
you’re leaving it up to the browser to determine the viewport size, which could
cause a disparity that you see here.