Removing space between widget and horizontal panel

GUI element

The inner rectangle you can see is a horizontal panel. and I have added 3 buttons into it. I want all these buttons to be places at bottom - most part of horizontal panel. I tried following line of code

margin-bottom: 0px;

but it has no effect on the buttons. Can anybody suggest me anything in regards of this?

Solution

There are two things you need to do

1) horizontalPanel.setSpacing(0); Reference : setSpacing

2) horizontalPanle.setCellVerticalAlignment(widget, HasVerticalAlignment.Align_Bottom); Refernce : setCellVerticalAlignment