The border property allows you to set a rule (line) around all four sides of your box in any color and thickness using a variety of line styles. Also, using additional border properties, you can independently set the borders on any of the four sides, giving you amazing design versatility. To set the border: 1. To set the border on all four sides, type the border property name in the CSS declaration block, followed by a colon (:) border: 2. Type a border-width value, followed by a space.