Editing stylesheets overview describes stylesheets in Bloom. Some advanced users can edit the stylesheets for collections or for books. You might need to get more help.
To edit a stylesheet, do these steps:
In the Collections tab, right-click a book and then click Show in File Explorer.
Find the customCollectionStyles.css or customBookStyles.css file.
Open it for edit in a simple text editor.
Add or change rules as necessary. If you paste rules into the file, be careful to not paste them in a location where they are "commented-out."
These topics have rules you can use or use as examples:
Save and close the file.