rgba(170, 0, 0, 0.8)

Every CSS color system has an optional alpha component that can define a color’s level of transparency. For example, to produce a background color of red that is halfway transparent for a <div> with an id of genera, we could write:

I’ve long found steps() a curious feature of the CSS animation specification. Rarely used in development and tricky to understand, I gave the feature fairly short shrift in my last book (Pro CSS3 Animation). However, steps() has a few perfect areas of application, and can be easily understood with the right analogies.