UHF-10808: Unit search component layout fixes

[teroelonen]

UHF-10808

What was done

• Make checkbox backgrounds on unit searches white
• Add select labels a class that allows them to look similar to other form labels

How to install

• Check installation instructions from the KASKO PR.

How to test

• Check testing instructions from the KASKO PR.
• Check that code follows our standards

Continuous documentation

• This feature has been documented/the documentation has been updated
• This change doesn't require updates to the documentation

Other PRs

• UHF-10808: Unit search component layout fixes #1087
• UHF-10808: Unit search component layout fixes drupal-helfi-kasvatus-koulutus#706

[github-actions]

⚠️ Visual regression found! Please check if this change is wanted or accidental. You can check the output here: https://city-of-helsinki.github.io/drupal-hdbt/pull/1087/html_report/