Finding what theme was used on a site
Permalink 1 user found helpfulYou can get more information on how the site was made here.
http://www.concrete5.org/about/showcase/community/non-profit/vancou...
In the article it mentions that a small number of marketplace add-ons were used. Everything else, including the theme, I imagine was all from scratch.
From the names of the CSS classes, you could easily find out, if the theme is based on a CSS framework like foundation or bootstrap - but they are wideley used, so this gives you just a hint if you cannot find a theme name itself.
When you check out a element on the page in develper tools, the class name might also give you the name of the add-on in use - backend-addons will not visible this way.
In the end, the theme could be custom-made, changed based on a marketplace theme or bought anywhere else on the web outside the marketplace - it might be difficult to identify or even impossible.
If you think about building a site that looks similar to the one that you are mentioning, just look at how the elements are stacked, how the CSS behaves (responsive?) and you will find that many themes are pretty similar from that point of view. Things like fonts, colors and style elements are really where "design" happens to make a framework-based-theme look different from others - but this might be just the stuff you dont want to "copy" - or your site will just look the same as the original.