Provide sensible integration of Carbon into the app

[nikku]

What should we do?

We want to ensure that Carbon components, such as the Variables Overview are properly integrated into the existing UI. The approach I propose is "theming", by overriding the existing Carbon variables.

• Ensure that Carbon integrates properly into the app, without averse effects (Welcome tab changes font size #4555)
• Consider customization so Carbon components fit into the existing UI frame

Why should we do it?

Ensure uses experience a coherent UI.

[barmac]

Moving this to the backlog as we are not deriving any value from this right now. It will be useful once we introduce more Carbon components to the app.

[jarekdanielak]

Related to bpmn-io/variable-outline#4 (that can possible be closed if we decide to tract this problem here)

[philippfromme]

Moving this to backlog for now. To be picked up whenever we work on the next Carbon-heavy topic.