Using a Custom CSS to Modify the Appearance of Content
You can use a custom CSS file to modify the appearance of your content instead of using Style Designer for HTML-based output formats. By using style names in your source document that match the classes defined in your custom CSS file, such as div.Heading1, you can make sure your content uses your custom CSS file. You do not need to create any other association between styles in your source documents and the styles in Style Designer. Make sure you define each tag and class from your generated output in your custom CSS file.
To use a custom CSS file with your project
Store your custom CSS file in the Files folder in your project.
Open your Stationery design project.
On the View menu, click Style Designer.
On the Project menu, click a target in the Active Target menu option that is an output format that supports this option.
In Page Styles, select the page style you want to modify.
On the Options tab, select your custom CSS file in Custom document css file.