Created attachment 464069 [details]
Screenshot of container element where outline is drawn both outside container and in the scrolled container content.

Steps to reproduce: 

Create a container element with `overflow:auto`, `perspective: 100px` and an outline.
Add content that forces the container to be a scroll container.
Add a positioned element that is translated in the Z direction and has z-index. I.e. `transform: translateZ(-100px)` `z-index: -1`.

Codepen here: https://codepen.io/johannesodland/pen/QWxeepe

Expected result:
Outline should be drawn right outside border edge of container..

Actual result: 
Outline is drawn outside border edge of the container, and in the content. See screenshot.