Refreshing my memory on setting position, I'm coming to this so late I don't know if anyone else will see it, but --
I don't like setting position using css(), though often it's fine. I think the best bet is to use jQuery UI's position() setter as noted by xdazz. However if jQuery UI is, for some reason, not an option (yet jQuery is), I prefer this:
const leftOffset = 200;
const topOffset = 200;
let $div = $("#mydiv");
let baseOffset = $div.offsetParent().offset();
$div.offset({
  left: baseOffset.left + leftOffset,
  top: baseOffset.top + topOffset
});
This has the advantage of not arbitrarily setting $div's parent to relative positioning (what if $div's parent was, itself, absolute positioned inside something else?). I think the only major edge case is if $div doesn't have any offsetParent, not sure if it would return document, null, or something else entirely.
offsetParent has been available since jQuery 1.2.6, sometime in 2008, so this technique works now and when the original question was asked.