Line Numbers Impossible To See in AdminCP Editor

[Shade]

FASTyle replaces default's codemirror with an enhanced version; usually uninstalling the plugin works just fine, but in your particular case, you are using a custom ACP theme which kinda interferes with FASTyle's codemirror version I suppose.

The solution is simple as restoring the original file, or blame your theme and work it out by overriding CSS rules.