The margin property

h1 {margin: 10px}
all four margins will be 10px

h1 {margin: 10px 2%}
top and bottom margin will be 10px, left and right margin will be 2% of the total width of the document.

h1 {margin: 10px 2% -10px}
top margin will be 10px, left and right margin will be 2% of the total width of the document, bottom margin will be -10px

h1 {margin: 10px 2% -10px auto}
top margin will be 10px, right margin will be 2% of the total width of the document, bottom margin  will be -10px, left margin will be set by the browser

• This property does not work with inline elements
• The "margin-bottom" property does not work with table cells

Note in IE 5.5 Beta 1:

• This property works with inline elements

Notes in Netscape 4.0+: 

• This property does not work properly with inline elements, input fields, images, and list items
• This property ignores negative values