CSS for Smart Connector UIExtension

[yentelmanero]

This PR is part of my bachelor research conducted in TU Wien in the Business Informatics Group.

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In this PR, CSS is provided for the Smart Connector UIExtension (more info in Client PR)

Client PR Server PR

[haydar-metin]

Thanks for the PR!

Somehow, the ECA is still not signed by your private email. I would recommend to commit only with a single email and to squash all your commits to have that single email.

Can you also add some description to your PR and reference the other PRs you have created, something like:

This PR is part of my bachelor research conducted in TU Wien in the [Business Informatics Group](https://www.big.tuwien.ac.at/).

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<Little Description>

<Other PR references>