How do we handle background on the body element?

[bokand]

e.g. See bug crbug.com/565930. If we don't resize the body, then a background on the body element wont fill the viewport.

First step is to see how this handles on Safari today.

[bokand]

background-attachment: fixed was the problem and Safari doesn't support that at all. The solution here is to continue resizing fixed attachment background even if there's no relayout.