The "Disable Sync" and the "Export as HTML" options are wrongly colored in "Dark" theme

[Softvision-MariusComan]

[Affected versions]:

• Firefox 58.0.2 and up

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• Have a Firefox profile with the latest version of the "Firefox Notes" add-on (3.0.0rc2) installed.
• You are logged into "Firefox Notes".
• Have the "Dark" theme activated from about:addons>Extensions>Firefox Notes>Dark.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites..
2. Click the "Notes" menu button from the bottom-right part of the sidebar.
3. Observe the options background color.

[Expected result]:

• All options have the same background color.

[Actual result]:

• The "Disable Sync" and the "Export as HTML" options have a lighter background color.

[Notes]:

• If you are not logged into "Firefox Notes", then only the "Export as HTML" option is affected.
• The issue is not reproducible with the TxP version of "Firefox Notes".
• Attached a screen recording of the issue: