I have two notes to add:
1. For the sake cohesion, I'd define a docinfo.html that only includes a custom css and then a CSS file, but you can do it inline in the same docinfo if you want.
2. Roles should add semantic and meaning to the text. They map to a CSS class and so you will use it to define styles. But I recommend to first defined them around concepts, like "important", "to_review" or "inline_example" instead of "bold", "blue_backgorund_with_yellow_bold_text". Once you define those, think how to display those roles and write the CSS.