Style the theme with custom CSS
Global level
Affects all pages.
Go to: Confluence Admin > Look and Feel > Stylesheet > Edit.
Global level with Refined
Affects all pages but it is packaged with Refined, meaning that if you uninstall or disable Refined, this will not be applied.
Go to: Refined Administration > Themes > scroll to the bottom of the page to find Custom CSS and HTML
Space level
Affects all pages in the active space.
Go to: Browse > Space Admin > Look and Feel > Stylesheet > Edit.
Permissions
Refined for Confluence acts a Confluence in general when it comes to permissions. Read more about who can apply CSS.
Examples
Hide Breadcrumbs
#rw_breadcrumb, #rw_page_breadcrumbs
{
  display:none !important;
}
Hide power by footer
#rw_footer
{
  display:none !important;
}
Hide dashboard button
#rw_category_menu li.rw_first
{
  display:none !important;
}