Wrong position when html element has offset and target is position fixed

[adamschwartz]

Repro steps:

1. Visit http://github.hubspot.com/drop/docs/welcome/
2. Open the console and apply position: relative; top: 100px to the html element.
3. Next apply position: fixed; top: 100px; left: 100px to a.drop-example-theme-social-sharing (“Share” button)
4. Finally, click the Share button and scroll the page. Observe that the positioning is off.

What I believe is going on is that the fixed positioning of the target prevents it from being affected by the top: 100px set on html. However, the values used to calculate the positioning of the Drop element (by Tether) are unnecessarily taking these values into account.

cc: @zackbloom

[uap-dev]

I am also encountering the same issue, however, I am using:

html { height: calc(100vh - 50px); }

I actually removed the offset and I am still seeing a 'jump' when the main content scrolls. Click Here to see it in action.