"Sync Your Notes" button doesn't have a hover effect after logging into the FxA

[SoftVision-CarmenFat]

[Affected versions]:

• Firefox 57 and up

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• Have a Firefox profile with "Firefox Notes" v2.0.0b7 installed.
• Log into a valid FxA.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites.
2. Hover the "Sync Your Notes" button and observe if any changes occur.

[Expected result]:

• The button displays a hover effect: its background color darkens a bit.

[Actual result]:

• Nothing happens, there is no hover effect.

[Notes]:

• The button has a hover effect before logging into the FxA account; also, the 3 dots menu button displays a hover effect after logging into the account.
• Here is a screencast of the issue:

[vladikoff]

Fixed in 54c7242