From SMTheming Wiki
fadetop command is used to fade the top of an element so that it disappears.
The dist parameter is the distance from the top, proportional to the height of the element, where the fade should start. 0 means no fading, and 1 means that the fade will go all the way from the top to the bottom.
To fade an element from transparent at the top to opaque in the middle:
To fade the top and bottom tenths of an element: