Embrace progressive enhancement

In previous chapters, we have considered the notion of progressive enhancement. It's an approach to development that I have found so useful in practice that I think it bears repeating. The fundamental idea with progressive enhancement is that you begin all your frontend code (HTML, CSS, or JavaScript) with the lowest common denominator in mind. Then, you progressively enhance the code for more capable devices and browsers. That may seem simplistic, and it is, but if you are used to working the other way around, then by designing the optimum experience and then figuring out a way of making that thing work on lesser devices/browsers, you'll find progressive enhancement an easier approach.

Imagine a low-powered, poorly featured device. It has no JavaScript, no Flexbox support, and no CSS3/CSS4 support. In that case, what can you do to provide a usable experience? Most importantly, you should write meaningful HTML5 markup that accurately describes...