Another alternative to Material Design would be IBM's Carbon [0], as far as boring enterprisey design systems go I find it criminally underused right now.
It's a great design system and implementing the visual design from scratch based in the guidelines helps a lot to understand the concepts behind it. At first it might look like overkill to implement six color schemes for the two light and two dark themes, but once you have this it's very useful to implement a visual hierarchy (using Carbon's layering model [1]) for the pages.
There are so many B2B enterprisey webapplications that do not have a good visual hierarchy, no hover and focus states, and no keyboard navigation. Instead they make buttons look like text, i.e. it does not look like you can interact with it.
[1] https://carbondesignsystem.com/guidelines/color/overview#lay...
*Update:* It's six not only five color schemes.