Fix default (text) colours

Problem/Motivation

Currently text colours seem incorrect or unset in some cases, e.g. links are blue.

I think the (text) colours used in the demo with different levels of gray are very universal and would be fine:
e.g. https://adminlte.io/themes/v4/tables/data.html

If changing other default colours—for example, for components and widgets—is also part of this task, I would prefer more subdued default colours than those shown in the demo.

Related documentation for colours:
https://adminlte.io/themes/v4/docs/customization.html

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes