### What problem does this PR solve?
Fix: Optimize styling and add a search settings loading state #3221
- Updated the calendar component's background color to use a variable
- Modified the Spin component's styling to use the primary text color
instead of black
- Added a form submission loading state to the search settings component
- Optimized the search settings form, unifying the styles of the model
selection and input fields
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
---------
Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>
