An example page that demonstrates the issue is available at http://jmoyer.nodomain.net/webkitbug.xhtml If an absolutely positioned element, such as the <body/> or its first child, specifies the "right" CSS property with a value of "0px" (and also top, bottom and left), the right side of the element's box moves farther from the right edge of the viewport as the device-width narrows, with significant effects observable on an iPhone 6 in landscape orientation with iOS 12.1.4 and also with Chrome 72.0.3626.119 (64-bit) when in mobile landscape emulation mode. One specific device width tested was 110, where the right side of the element/content isn't even halfway across the viewport. As mentioned in the title, this only occurs with smaller widths of device-width in the viewport <meta/> and pages render correctly in desktop mode, regardless of the viewport width. The upshot of the expected behavior is that content should fill the width (100%) of the viewport and not 66% or 50% in both desktop and mobile rendering modes. Current versions of Firefox and IE were able to render this content as expected.
You know, looking into it further, it happens even with statically positioned elements, as the updated example shows.
Sorry, this bug is confounding to me. It is real, despite my thinking otherwise for a moment. viewport widths of less than 253 for the included sample, but the problem can be magnified or compounded with other, more complicated stylesheets.
<rdar://problem/48789960>