Gmail ignores the entire margin or padding declaration if there is a negative value.
margin:-40px 10px 0 0
margin:40px -10px 0 0
margin-top: -40px
margin-right: -40px
padding-right: -40px
padding-top: -40px
Gmail does support negative values in the generic padding property - this is not recommended however because Yahoo New and Classic do not support negative values at all.
