In CSS, you will come across some shorthand notation for the margin, border-color, border-style, border-width, and padding properties. It isn’t obvious or easy to remember which token in the value applies to which side of the element so here’s a handy list of the 4 possible varieties:
- One token — all-sides-use-the-same-value
- Two tokens — top-and-bottom right-and-left
- Three tokens — top right-and-left bottom
- Four tokens — top right bottom left
At least the four-token example can be remembered by associating the element with a clock where time progresses clockwise.
Source: http://formattc.wordpress.com