It is time to explore color a little more deeply. Add the following color styles for the body element and the .thumbnail-item class in styles.css.

body {
  font-size: 10px;
  background: rgb(149, 194, 215);

a {
  text-decoration: none;

.thumbnail-item {
  border: 1px solid rgb(100%, 100%, 100%);
  border: 1px solid rgba(100%, 100%, 100%, 0.8);

You have declared values for the .thumbnail-item’s border twice. Why? Notice that the two declarations use slightly different color functions: rgb and rgba. The rgba color function accepts a fourth argument, which is the opacity. However, some browsers do not support rgba, so providing both declarations is a technique that provides a fallback value.

All browsers will see the first ...

Get Front-End Web Development: The Big Nerd Ranch Guide now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.