Handle SCSS deprecation warnings

[oliverschuerch]

There are a lot of deprecation warnings around, when you start the docs. Try to get rid of them.

### Tasks
- [ ] Invest time to investigate and find out how quickly these issues can be resolved
- [ ] After fixing the issues, remove the `silenceDeprecations` properties in both packages (styles and documentation)

To see them do the following steps:

1. open up styles/gulpfile.js
2. remove all silenceDeprecations: ['mixed-decls'] occurrences
3. run pnpm styles:build

To do the same in the documentatoin do the follwing steps:

1. open up documentation/vite.config.js
2. remove all silenceDeprecations: ['mixed-decls'] occurrences
3. run pnpm docs:start