Theme title displays entire file’s contents

I manually edited my style.css file for my theme and now the title of the theme in the presentations section of the admin panel appears to be displaying the entire content of the file – which of course is very long. It will not allow me to change anything with it through the admin panel, because the file name is too long to put in the url. My guess is there is a simple tag that I have accidentally removed, but I haven’t been able to find anything about this. Anyone know how to fix this? Thanks!