fix(sass): added calc to prevent deprecation

[peter7cole]

Description

• This PR addresses a Deprecation Warning that we've noticed in our builds for the Webex admin portal.
• Linked announcement here: https://sass-lang.com/documentation/breaking-changes/slash-div
• The automatic migrator (sass-migrator on npm) had some deal-breaking errors for me, so I went through by hand

Related Issue

Deprecation Warning: Sass Slashes #1176

Motivation and Context

We would like to clear our warnings

Screenshots:

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.