You can import an existing CSS or SWC file instead of specifying style settings in Guide Builder so that the form guide follows style conventions that you use in multiple form guides or in other documents.
If you import a custom styles SWC file, editing the styles affect all other form guides that use that SWC file. If the SWC file is a third-party format, it will be replaced with a default guide version when you save it. If you import a custom CSS file, you must use the same class names and attributes as Guide Builder.
See also 

To use custom styles