For themes and custom CMS setups, the typical HTML theme is not ready to go at all but here are some common sed commands (search and replace that will get most of them working without breaking as you'd expect).
The problem is that often the theme directory will be separate from the content and this will break the relative paths that these themes use.
sed -i s/'href="'/'href="/themes/yourtheme/'/g index.html
sed -i s/'src="'/'src="/themes/y........