You are going to have to add custom CSS stylesheets to your page, and for that you will need to use a template. Since you seem to be generating standalone output, you can use json_items or components to embed your Bokeh content in a simple page that has the extra CSS stylesheets at the top. You can use your browser to inspect the page elements to know what CSS selectors to style, or potentially you can set css_classes and add selectors that style based on those classes that you add.
SOLVED: I made it work! Thanks, I’m not sure what the issue was but it’s working now with css_classes. There is another issue now with a white margin in the html that I don’t know how to change to black.