I have no idea what happened but basically my css stylesheet with 1000 lines has turned into a single line stylesheet.
Questions:
1) Why has it happened?
2) What can I do to revert it back as I don't have any recent backup.
Thank you
Must be because the program you are using ¿? has a CSS compressor somewhere...
Depending on to many things, you could get the original CSS file.
If you can't, try to beautify the compressed one. Here you have a few online tools to do'it.