includes/templates/nouvel/css/stylesheet.css
Is the stylesheet being called on page load but this is the contents of the stylesheet.css located at this location:
Code:
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<HTML><HEAD>
<TITLE>500 Internal Server Error</TITLE>
</HEAD><BODY>
<H1>Internal Server Error</H1>
The server encountered an internal error or
misconfiguration and was unable to complete
your request.<P>
Please contact the server administrator,
[email protected] and inform them of the time the error occurred,
and anything you might have done that may have
caused the error.<P>
More information about this error may be available
in the server error log.<P>
</BODY></HTML>
It appears that this is not a complete enough stylesheet to actually apply any styling. Try for starters, copying the includes/templates/classic/css/stylesheet.css file to your includes/templates/nouvel/css/ folder and see if things do not improve.
You might also need to copy the /includes/templates/classic/images folder