wget --mirror --convert-links --adjust-extension --page-requisites --no-parent https://site-to-clone.com

• --mirror make the download recursive.
• --no-parent Do not crawl the parent directory.
• --convert-links makes all the links work properly with the offline copy.
• --page-requisites download JS and CSS files.
• --adjust-extension add the appropriate extensions (e.g. html, css, js) to files if they are missing.