Hello,
The style are not gone, but you have a php error somewhere on the page...
So, could you first check that you don't have a view override for iCagenda in your site template "html" folder (com_icagenda) ?
If yes, so remove or update it
Then, if not, gor to your Joomla configuration, then turn ON the error reporting on "Development".
Go to the page, and check for any error/warning PHP messages display (with file and line of the error).
Copy/paste here the error messages (but remove the first part of the path, to not have your server path).
And set back error reporting on "default" or "none" (recommended setting on live site, as other settings are for debugging/development only)
Thank you!
Best Regards,
Cyril