How do Web Developers work securely and have things like automatic backups?

I'm a student and currently an amateur web designer & developer. I have all my repositories on my external hard drive and work on them with a USB Web Server and a Portable version of Notepad ++.

Today my program stopped working and wiped my CSS file. I have backups but the 3 hours of work I did is gone and it could've happened on something even more important.

I've written this question to ask fellow experienced developers what's the best way of working securely and port-ably with automatic back-ups and things like that, what is the best way to approach this sort of work? Is there a cloud based solution I should be using or something?

I've heard of GitHub before but I'm not sure if this is the sort of thing I should be looking for.

Thank you for reading my question!