CSS resources can be added to the Concordion output using an extension. The CSS can either be:
An extension with embedded CSS is installed.
When Concordion is run, the CSS is embedded in the <head> section of the output HTML.
An extension with linked CSS is installed for the CSS file
my.css with the target location
When Concordion is run,
/css/my.css is available in the Concordion output directory,
and a link to the external stylesheet
css/my.css is declared in the output HTML.