Small dynamic units improvements

What does this MR do?

Introduce some more relative font-size unit usage, and fix a browser problem related to select element width

How confident are you it won't break things if deployed?

100%

Links to related issues

• closes #1001 (closed)
• CSS last adjusted in ef217ce2

How to test

• log in as store manager or higher
• view store page in various browsers, font size settings and zoom levels
• check #1001 (closed) in Chrome for pickup-edit width

Screenshots

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• use "state:" labels to track this MR's state until it was beta tested
• added an entry to CHANGELOG.md

Release Notes

In manchen Browsern wurde beim Bearbeiten von Abholzeiten die Uhrzeit nicht vollständig dargestellt. Das haben wir behoben.