Atlassian Description: "Defines the appearance of the dashboard and a user's profile."
Found In: Confluence Administration -> Look And Feel -> Layouts -> Main/Space/Blogpost ... Layout
This is where You define the look of Pages, Spaces, Blog Posts etc for all objects in the Confluence Site. Please also notice these can be changed per space, not recommended, refer to Layouts
Notice, the editing is directly and there is currently no versioning, so be carefull 
As this is not via the RTE, scipting (like in Macro(s) ) are used, and rendering a Macro is like:
$helper.renderConfluenceMacro("{jiraissues|max=100|page=10}")
Hence Macro and Wiki Markup in a mix..
Scopes for Confluence CSS Styling