TRBL for padding and margin shorthand

Stay out of "TRBL" (top right bottom left) for padding and margin shorthand.

Values that are present are used to fill in for values that are not:

• padding: 1px 2px 3px 4px
  
  T = 1px; R = 2px; B = 3px; L = 4px
• padding: 1px 2px 3px
  
  T = 1px; R = L = 2px; B = 3px;
• padding: 1px 2px
  
  T = B = 1px; R = L = 2px;
• padding: 1px
  
  T = R = B = L = 1px