Refactor: Migrate Sass to be 2.0.0-friendly

### Description

The latest dependency bump led to the following build warnings:

```cli
DEPRECATION WARNING: Using / for division is deprecated and will be removed in Dart Sass 2.0.0.
```

We should migrate our style files to be Sass 2.0.0 ready. The following are some changes that will be needed:

* [ ] use `math.div` instead of `/`
* [ ] use `@use` (and `@forward`) instead of `@import`

### Proposed Advantages

Prevent moving to the latest dependencies when they move to Sass 2.0.0.

### Relevant Info

Sass provides a migrating tool to help with this: https://sass-lang.com/documentation/cli/migrator

Dependencies that use Sass will likely also need to be updated (e.g., [`calcite-base`](https://github.com/Esri/calcite-base)).

Start by locating the repository's Sass style files and dependencies that use Sass, including calcite-base, then review the Sass migrator documentation. Migrate division and module syntax as needed, and verify that the build no longer emits Dart Sass deprecation warnings and remains compatible with Sass 2.0.0.

Written by the indexing model from the issue text.