Fix CSS math calculations deprecation warnings

[Riley Wong]

The style sheets use a deprecated math calculation such as $border-radius-root / 2 when instead it should use calc($border-radius-root / 2) for good practice. The site still works and builds, but it would be nice to tackle these warnings.

Updating the bootstrap styling itself (I believe Vuetify) might fix this, but it may not be easy because packages might conflict.

These may need to be manually replaced.