We have some javascript in place that prevents fixed backgrounds images from rendering as fixed on touch screen devices, like the Pixelbook. We do this because there are some known repainting css issues caused by fixed background images on elements (it’s also really heavy on CPU’s).
A work around which you can try is set a Fixed element as the background, try the following:
Add in a div, call it “Fixed background” (or whatever you wish)
Set the div to Position: Fixed
Width: 100%, Height: 100vh (type in 100vh so that it takes up the full viewport)
Adjust the z-index of this element to sit behind all other elements