You can create custom error messages instead of using the default and very ugly, plain jane Apache error messages. Much more professional. Here is the line(s) to add to your .htaccess file:
ErrorDocument XXX /XXX.html
You need to create the XXX.html pages in advance. They can be any files or file types, or you can just point to a directory. Replace XXX with server HTTP Status Code. Some example and common error codes:
Similar to 403 Forbidden, but specifically for use when authentication is required, and has failed or has not yet been provided.
The request was a valid request, but the server is refusing to respond to it.
404 Not Found
The requested resource could not be found but may be available again in the future. Subsequent requests by the client are permissible.
500 Internal Server Error
Miscellaneous server error (usually better documented in the server error log).
Last Revised: 2015-08-31