text: Title: Configure theme (e.g. primary color?)
  Body: Hi folks,
  
  Loving jupyter-book (migrating here from quarto) but I am struggling to customize the theme, e.g. by setting the primary color.  I've tried various ways I've seen suggested for doing this:
  
  - [custom css variables](https://sphinx-design.readthedocs.io/en/latest/css_variables.html)
  - I've trying to add a custom `_sass/theme.scss` redefining `$primary`
  
  but haven't had any luck overriding this.  
  
  It seems that some sphinx themes provide a mechanism to set colors in the conf.py; it would be great to be able to do something similar in jupyterbook configuration yaml or with a custom sass. (compare to [quarto theming](https://quarto.org/docs/output-formats/html-themes.html#theme-options)).  I'm only familiar with how other static site generators have handled this, I'm not experienced enough in css, sass or sphinx to figure out how to alter the behavior here though!  
  
  