Request: change volume OSD background color to light in light variants

[claytonwramsey]

Hi! Thanks again for this great theme :).

The volume slider OSD which appears when pressing the volume keys has a dark background, even on light variants of Lavanda. It looks a little out of place:

I was able to fix this by altering the definition of $osd in src/sass/_colors.scss to the following:

$osd: if($variant == "light", background(a), background(f));

[claytonwramsey]

I found a better approach which doesn't also make the overview white. I made the following edits to _osd.css:

%osd_panel {
  // color: on($osd, secondary);
  // background-color: $osd;
  color: rgba($black, 0.6);
  background-color: $background;
  /* other properties below */
}

[claytonwramsey]

I switched back to my original approach from the first post. Note: Because some text (esp. in _app-grid.scss, _search_entry.scss, and _search_result.scss use forcibly black text via on(black), they also have to be replaced with on($osd).