fix(safari): basic dark mode support

[dskuza]

Fixes #201

Goal

Fix #201: basic launcher dark mode support

Todos:

• [X] Remove explicit background color
• [X] Update assets for any / dark modes

Implementation Decisions

Assets were taken from design here and updated within the project to add support for dark mode. By removing the explicit background color, the launcher takes the color of the window based on the selected system theme (i.e white for light, black for dark).

All Submissions:

• [ ] Have you followed the guidelines in our Contributing document?
• [X] Have you checked to ensure there aren't other open Pull Requests for the same update/change?

[dskuza]

@nzeltzer @collectedmind please add the correct label(s) / project(s) / milestone(s) as required

[nzeltzer]

@dskuza Let’s get Jen’s eyes on this before merging.

[dskuza]

@nzeltzer Re-review requested as I made a change to explicitly set window color for OSes < 10.14 (when dark mode was introduced).