* DEV: Fix SCSS deprecations
Followup to https://github.com/discourse/discourse-subscriptions/pull/171
Also fixes:
```
╷
581 │ hsl(random(360), 100, 50);
│ ^^^^^^^^^^^^^^^^^^^^^^^^^
╵
/Users/pmusaraj/Projects/discourse/discourse-subscriptions.scss 581:7 root stylesheet
Deprecation Warning: $lightness: Passing a number without unit % (50) is deprecated.
```
* More cleanup
Sample warning was:
```
Using / for division outside of calc() is deprecated and will be removed in Dart Sass 2.0.0.
Recommendation: math.div($sidebar-height, 1.2) or calc($sidebar-height / 1.2)
More info and automated migrator: https://sass-lang.com/d/slash-div
```
