I’ve messed up the mobile view of my site!

CSS Hero is powerful in enforcing your desires: sometimes too powerful.
If you try to do too much for your CSS knowledge, first thing you’ll do is destroy theme responsiveness.

A classic – even when writing manually CSS code.

Minimalism of your edits is the key. Little and smart CSS is sufficient.

We wrote an article which might be of help: avoid rookie mistakes.

Check out the Desktop Only feature especially and consider it for your edits that break site responsiveness.
You can apply it selectively too to your old edits too. Will be a bit a PITA – but it’s much better than nothing.

Another link worth checking out for understanding how to make most out of the responsive features of CSS Hero in here