My personal site/portfolio done with Middleman.
Done using the latest HTML5 and CSS3. It is fully responsive and makes extensive use of semantic HTML and CSS Flexboxes.
I haven't tested it on these, but I suspect it will obliterate any browser older than IE 9 or 10.
If you like the site, feel free to fork it, redress it, whatever. It's MIT licensed.
Requires Ruby 2.1+ and all the gems in the gemfile.