When you want to customize the appearance of Announcements, KB Articles
In this situation, you must precede each your custom style definition with a special parent selector specified for the style sheet in question (e.g. #announcement for the Announcement style sheet). This parent selector ensures that your style definition applies only to the user content, not to the entire web page. All default style sheets contain those parent selectors.
See the parent selectors for different objects:
For Announcements: #announcement
For Preview Pane: #preview
For Knowledge Base Articles: #kbarticle
For Service Catalog Items: #servicecatalog
To specify the style for a particular web page element, add the element's code after the selector. For example, to set the font for Announcement paragraphs (p), use the following code:
font-family: Arial, Tahoma, Helvetica;
In the same way, you can specify the style for other elements: headings, lists, tables, etc.