Troubleshooting Missing CSS/JS in the Control Panel
You’re trying to install Craft for the first time and the installer isn’t loading CSS or JavaScript. Or maybe you view your browser’s inspector and the response to the CSS/JS files are all garbled.
Chances are you have zlib.output_compression enabled in your php.ini file and you need to disable it. This is most likely related to this PHP bug report.
Even if you’re not getting garbled CSS/JS in the response, you might see this error as in your browser or in the response for the CSS/JS:
Failed to delete buffer zlib output compression
The fix for that error is the same.
You will probably have to restart your web server for any changes to the php.ini file to take affect.