wget tem uma opção
--adjust-extension que irá adicionar as extensões corretas aos arquivos HTML e CSS.
If a file of type ‘application/xhtml+xml’ or ‘text/html’ is downloaded and the URL does not end with the regexp ‘\.[Hh][Tt][Mm][Ll]?’, this option will cause the suffix ‘.html’ to be appended to the local filename. This is useful, for instance, when you’re mirroring a remote site that uses ‘.asp’ pages, but you want the mirrored pages to be viewable on your stock Apache server. Another good use for this is when you’re downloading CGI-generated materials. A URL like ‘http://site.com/article.cgi?25’ will be saved as article.cgi?25.html.