Each theme for Oracle Content and Experience must have a design, which specifies the look-and-feel of pages and style settings for components used in the theme.
When users create a site, they must select a template which includes a theme by default. You can create or choose to use a different theme for a site.
When creating a theme, along with designing page layouts you must specify the available styles that will be displayed in the Settings panel for each component type that will be available to users (Paragraph, Title, Image, and so on). There can be multiple styles within a design to specify the default settings for different components. You make choices for text fonts and font sizes, image framing, and so on, then save them as a named design. The items in the design influence the look of the page layouts when rendered.
See Work with Site Pages in Building Sites with Oracle Content and Experience.