We have three blocks of text, each with a heading, a short paragraph, and a link. In screen sizes of approximately tablet width or more, we would like this content to be laid out in three columns. In narrower screen widths, the content will organize itself in one full-width column.

Take a moment to visit and read the documentation for Bootstrap's mobile-first responsive grid. You can find it at http://getbootstrap.com/css/#grid.

In short, the grid is based on a 12-column system. The basic class structure allows us to use a class of col-12 for full width, col-6 for half width, col-4 for one-third width, and so on.

Thanks to the creative use of media queries, Bootstrap's grid can be very adept at responding to different screen sizes. Recall that we want our welcome message to have a single-column layout up for screens to tablet-size, and then adapt a three-column layout at approximately 768 px for larger screens. Conveniently, Bootstrap has a built-in breakpoint at...