Translations:New Template System in LS3.x/135/en

so you should use the very same syntax as the package's file (eg: "awesome-bootstrap-checkbox.css" alone without it's folder path would not work). You'll find the complete list of core packages and their files in /application/config/packages.php and config/third_party.php. For example, for awesome-bootstrap-checkbox.css: https://github.com/LimeSurvey/LimeSurvey/blob/2398dda3b425da1a37d4611cd7963d39ac739987/application/config/packages.php#L54-L56