When I first started learning web development in earnest, (beyond basic HTML), the community college I was attending was still teaching Dreamweaver as de facto method of building a site and using Photoshop and tables based layouts. Meanwhile I had launched my first blog with WordPress, fresh off the 1.5 release that brought full themes, XHTML and CSS. Reading blog posts on the subjects was basically the way I learned those skills. And viewing the page source of the authors writing those posts.
Fast forward to 2016, and I still view source. More often than not now, I’m learning from GitHub repositories. Which is why finding the Octotree browser plugin was such a find. Rather than having to navigate back and forth inside a repo, you get a tree view of the files to the left of the browser window. If you find your self using the back button and navigating breadcrumbs, I highly recommend checking it out.