I am wanting to use wordpress.com to host a blog of mine & so save myself updating/etc. effort.
Unfortunately it uses some specific CSS code that is essential to the point of the post.
I've read comments requesting wordpress.com to allow people to edit the CSS of themes - which would be complicated as each user would end up with their own twiddled versions of the theme files.
However, if you find a method of inserting header information & make that customisable you could achieve much the same effect:
* CSS can be overruled (if customised after theme CSS)
* CSS can be called in from remote source
Useful and doesn't require theme-editing.