scrollbar does not accurately track the contents

[vapier]

open a very large file like:
https://logs.chromium.org/logs/chromeos/buildbucket/cr-buildbucket/8768055427601581345/+/u/install_packages/chromeos-base_chromeos-chrome_log?format=raw

try to use the scrollbar. it's difficult to grab in the first place, but once you do, trying to scroll to the bottom doesn't follow the mouse cursor. guessing there's some math/rounding error that is exacerbated by longer files.