I am certain that there is no CSS for J2ME, you could implement that but I don't think it is a good waste of time, and maybe there is no other implementation like this because using ready components from midp we only get the themes from the cellphone to decorate our applications.
Alternatively you can develop your own canvas based gui that supports themes. I have just just finished a beta version of an app that uses customisable themes for the app. You require a new Nokia device to use it. Check it out. http://www.getjar.com/software/Java/All/Search/youmenow
No licence fees required if you make your own components.