I joined several of my Sparkbox teammates this month a helped write a joint article for The Shift on the topic of Progressive Enhancement. I love the topic and I dive into what I love about CSS, the cascade makes progressive enhancement a natural aspect of the development process. The tl;dr on utilizing the cascade for progressive enhancement is to put styles for older browsers near the top of the selector block with newer properties toward the bottom. This works especially well for Flexbox properties, which I get go into detail in the article, so check it out!
Be sure to keep up with what others are writing for The Shift, with my list of Shift articles.