Improve error handling when user variables are unset

[bonk1t]

• Improve error handling when user variables are unset
• Fix minor css issue for inactive model selector

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.81%. Comparing base (ed6a4ac) to head (bf1ad84).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #89 +/- ## ========================================== + Coverage 96.79% 96.81% +0.02% ========================================== Files 62 63 +1 Lines 1716 1727 +11 ========================================== + Hits 1661 1672 +11 Misses 55 55 ```

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