10up has released a WordPress component library, which is, “a collection of front-end components constructed with WordPress and accessibility at the forefront.” Jon Bellah says that each component in the library is WCAG 2.0 accessible, and they’re hoping to make developers’ lives a bit easier when it comes to WordPress-specific components.
I really love this, because it’s not just HTML and CSS, but corresponding WordPress functions that all of us would use. I’d highly recommend this as a learning resource for aspiring and current theme developers; 10up has put these kinds of components through the paces in their many years of client work.