Pull To Refresh - Action during pullend

It’s easy to get the CSS translate value during pullmove on a ptr-content item. I’m using it to draw a background behind the view as it drops down, in-line with the current position of it.

But my problem is in creating a function to ‘undraw’ (or, reverse draw) the background so it shrinks back at the same rate as the view snapping to return to the top of the viewport.

Is there a specific CSS animation value that the pull-to-refresh content is using to return to the top? Or, is there a queryable property that will tell me what the translate value is on the way back up (when it isn’t being pulled down manually)? Scrolltop returns 0 and translate doesn’t update after the mouse/touch releases.