Problem/Motivation
Since we don't need to support ie11 any more, let's start moving the Umami theme to a more modern CSS base.
I forsee lots of heartache with conflics and re-rolls, if we try to tackle this issue while we are also tacking #2936875: Umami Theme - follow-up - remove elements, use classes in CSS, so let's get that committed first.
Steps to reproduce
None
Proposed resolution
Minimum: Rewrite the Umami theme colours to use css variables
Nice to have: do the same for paddings/margins/etc
Remaining tasks
Do it
User interface changes
None
API changes
None
Data model changes
None
Release notes snippet
Umami theme is now using CSS variables instead of hardcoded values for many of its CSS properties.