[Enhancement] "Price Wise" door hanger should respect the coloristics of the browser's dark theme

[SoftVision-CarmenFat]

[Affected versions]:

• Firefox Release v63.0.1 and up

[Affected Platforms]:

• All Windows
• All Linux
• All Mac

[Prerequisites]:

• Have a Firefox profile with the latest version of the "Price Wise" add-on (9.0.0) downloaded from (download link).
• The browser's theme is set to "Dark" from the about:addons "Themes" section

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites.
2. Click the "Price Wise" toolbar button and observe the door hanger.

[Expected result]:

• The door hanger respects the coloristics of the browser's dark theme

[Actual result]:

• The door hanger doesn't respect the coloristics of the browser's dark theme

[Notes]:

• Here is a screen shot of the issue:

[Osmose]

The present graphic would need to be redone for dark mode by design. Most of the rest of the icons and colors we can crib from the photon style guide and browser chrome.