The whole configuration of the plugin is available through the constant editor. Please see the Configuration section for more details.
You can override the settings made from the extension manager about the CSS directory through the page TSConfig. In order to do this, edit the properties of a page, and place the following code in the TSConfig field:
tx_cssselect.cssDir = path/to/a/directory,path/to/another/directory
Specified paths are relative to the TYPO3 site path.