Replace chakra-UI with Sass

[antonykamp]

Describe the solution you'd like
It would be awesome if we could remove chakra-UI completely and replace it with Sass.

Describe alternatives you've considered
Other possibilities were tailwind or bootstrap. But I'm not sure whether we should change it, because of the principle "never touch a running system".

Additional context
If we use Sass, we could move the look and feel from your web app to emails (see #76 )

[antonykamp]

Otherwise, we're going to have much more overhead by separating style and structure. entel.me isn't a simple one-page-website. Style and structure are strongly connected.
Otherwise, we would have shorter and more readable .tsx files by introducing Sass. :/