Web Design in a Nutshell, 3rd Edition

The side-specific and the shorthand border properties may include a border-style value, a border-width value, and a border-color value. They do not need to be in any particular order. You do not need to declare all three border qualities, but keep in mind that if the border-style is not declared, there will be no border.

The border shorthand is somewhat different from the other shorthand properties discussed so far in that it can be used to apply border properties to all four sides of the element only. It does not provide a way to target certain borders and there is no system of value replication.

The rules listed here are all valid examples of the border shortcut properties.

    h1 {border-left: .5em solid blue; }
    h1 {border-left: solid blue .5em; }
    h1 {border-left: solid .5em; }

    p.example {border: 2px dotted #666633; }
    p.example {border: dotted 2px; }