Refine CSS to functional style

[KochTobi]

Description of the issue

The frontend development is slow due to styling being crafted for every page separately. When implementing new solutions and wanting to apply existing styling, one has to dive into the CSS to discover how comparable elements in the UI were styled.

Solution you would like

Have functional classes in the css that can be applied to achieve specific effects. Something like class="dialog large" or class="dialog small" or class="tag" class="tag danger"

Other solutions considered

Styling in Java code again. As this would warrant specific java classes and a strict class hierarchy, I think it should be avoided for functional styling.

[sven1103]

Big topic, I suggest we split this in smaller chewable chunks. Will start with the first reference issue, which will tackle dialogs and link it back to this PR.

[sven1103]

Referencing dialogs: #914

[github-actions]

This issue is stale because it has been open for 30 days with no activity.