We'll look at the CSS to create the above results a piece at a time, so we can review the interesting parts one by one.
The .wrapper class is used to assign styles to the <div> that encloses all of our other content. This establishes thesize of the container using width and height as well as its margin and padding.
Of more interest to our discussion here is the use of the border property to establish a border around the outside edge of the element. This border is a solid line, 6 pixels wide, in the color mediumturquoise.