background-position-y: value;
object.style.backgroundPositionY = "value";
<'background-position-y'> = [ center | [ [ top | bottom | y-start | y-end ]? <length-percentage>? ]! ]#
<length-percentage> =
<length> |
<percentage>
<length>
Specifies the length using a number followed by a unit of measurement.
<percentage>
Specifies the percentage using a number followed by a percent sign (%).