How to fix WP dashboard loading without CSS or with broken stylesheet.
- Empty browser cache (or load the page preesing CTRL+F5).
- Clear all cookies.
- Disable all caches.
- Update all plug-ins and themes.
- Deactivate all plugins and re-activate one by one (you can deactivate those by adding something like 0 for each file name).
- Add to wp-config.php file the following.
If those doesn’t help, you can try increasing “PHP Max Input Vars” value from 1000 to 2000. you can do it by editing php.ini or if you are using Plesk, you can do that from Domains > example.com > PHP Settings and add to Addition Directives
max_input_vars = 3000