Cascading Style Sheets

Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation of a document written in a markup language like HTML. CSS is a cornerstone technology of the World Wide Web, alongside HTML and JavaScript.

You can use it to customize the appearance of your GnuCash reports and also some elements of its user interface.

One approach to start using it

Export the printable/easy/fancy invoice to .html and open it using i.e Firefox -- then inspect the html with its developer tools and modify css until you find a satisfactory result. the custom css can then be inserted into the report option and saved as a custom report. from IRC