(There is probably a task about this already, but Phabricator search being what it is, I'll take my chances.)
There are multiple reasons why maintaining community-controlled styling of templates and other interface elements is hard:
- CSS is just not a very nice language
- there is no way to share styles without copy-pasting
- there is no way to reuse MediaWiki style properties (e.g. make infobox borders the same color as ToC borders) without having to manually follow changes
In web development, such problems are customarily solved by using CSS preprocessors (MediaWiki core uses Less). We should strive to provide the same support for editors as well.
This could be done via MediaWiki:*.less pages, or template styles (after T133410: Deploy TemplateStyles to WMF production), or both.