Improve scaling/sizing behavior of web UI

[klieret]

The web UI should always fit on the page even when the controls of the top bar are expanded. The three sub-panes should be sized accordingly.

[!tip] General tips for frontend contributors:

• Please open a separate PR for every issue that you address. Try to keep PRs small and concise (if you're thinking of bigger refactorings, please let us know)
• In the web UI under "Extra Settings" there's a switch to run without needing API credits for testing purposes
• Please install pre-commit (pip install pre-commit && pre-commit install) to ensure that your submission follows the styling guidelines