Refer to the Visual LANSA User Guide for how to Register Individual External Resources or the Developer Guide for how to Register Multiple External Resources and then Using External Resources with WAMs for how to link them to your Weblets.
You can add scripts and styles external resources to both webroutines and weblets. The standard practice is to add the CSS stylesheets that provide the theme (See Theming WAMs) to your site layout and scripts and other styles to your webroutines or weblets as required.
The WAM runtime consolidates the scripts and styles so that they are only added once to the output page. Refer to Order of External Resource Inclusion.