https://sass-lang.com/documentation/breaking-changes/slash-div
> Sass currently treats / as a division operation in some contexts and a separator in others. This makes it difficult for Sass users to tell what any given / will mean, and makes it hard to work with new CSS features that use / as a separator.
There's a handy migrator:
npm install -g sass-migrator
sass-migrator division **/*.scss
And it cleverly avoids the need for the ugly division method in most cases.