How is the CSS added to the Help File
CSS can be added to the help file by clicking Add Style Sheet on the main menu. That will open up a page for entering a large text file. You can paste it in or type it in there. When you are finished, click done and the style sheet becomes part of the project.
In addition, when you open up the visual editor, it will be styled to the same background and text color that you chose in the css for all future topics.
At run time, it is added to the page as its about to be displayed by the Help Viewer. It is put in the head section of the document between style tags. It is not added until it is time to display it to conserve space in the help file. So the help topics share the style sheet much like an external style sheet is used in regular html pages. The difference is the style sheet is stored inside the Help Writer project file.