UI fixes

[mawinter69]

• wrap the checkboxes in a flex container so the categories are properly rendered in the throttle step and have enough space in between
• remove the blockwrapper, it's not needed anymore
• make the input fields a number
• make category name mandatory

Before:

After:

Testing done

Interactive testing

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed