In Microsoft Word and HTML documents, you can use styles to apply paragraph formats (such as indentation and spacing) and character formats (such as font styles and colors) to give your documents a uniform appearance. If you apply styles consistently, any change you make to a style definition will be propagated throughout the document, and the affected regions will be updated accordingly. Styles are also used in Word's outline view to specify the hierarchy of paragraphs within a Word document.
Any paragraph or character style that has special help-authoring behavior should have a matching style in the Doc-To-Help project in order for it to work correctly in your help target. Styles used for appearance only do not need to be in the Doc-To-Help project.
Doc-To-Help provides many predefined styles, which are added to a project by default. If one of the predefined styles cannot be used, you can create your own paragraph and character styles, but you must define a matching style within the Doc-To-Help project. Through those matching Doc-To-Help styles, you define the behavior of the compiled Help system. Please note that this is an advanced feature, and creating your own styles is not usually necessary.
For more information on defining styles in Microsoft Word, see Working with Styles in Word or consult your default HTML editor's documentation for information on defining styles in an HTML document.
More:
Importing Styles from a Word or
HTML Document, Template, or Cascading Style Sheet
Importing Styles From Another Project