WordPress code editor messed up my code!

This isn’t as good as line numbers but you can add a dummy class every so often.

#_________section_1 {
    display: none; /* Just in-case it strips the empties */
};

It may help you to quickly scroll to the relevant section. To be honest though, you should have a mirror of your site stored locally and only change the online version when you’re 100% satisfied.