How to use jquery plugins for custom Redmine theme

Dear Redmine community,

I successfully can already use some jqueryUI widgets (like calendar picker or tooltips) but changing the look of other inputs like checkboxes, drop down menues, etc. is not supported natively by now.

How can I use external jquery plug ins for styling the rest of the inputs? Just copying the css / javascript in the necessary files (application.css + theme.js) doesn't work.