Loading spinner has a ~1px wide white line visible around it on dark theme

[dkasak]

Description

As the title says, the spinner (e.g. when joining a room) has a thin, dotted white line around it, visible only in some frames, which rotates with it when using the dark theme. This is on latest Element Web.

Steps to reproduce

1. Set dark theme.
2. Try joining a room (or equivalent action which shows the spinner).
3. If the problem doesn't appear, try doing it a few times and/or zooming the page in a bit (not sure if it's necessary).

Version information

• Platform: web

For the web app:

• Browser: Firefox 89.0.2
• OS: Arch Linux
• URL: app.element.io (1.7.33)

[t3chguy]

Duplicate of #17642 - this is a Firefox bug with masks and transformations