down_btn = new JButton( "Down" );
down_btn.setMargin( btn_insets );
down_btn.setToolTipText( "Scroll Downward by half a screen" );
down_btn.setMnemonic( KeyEvent.VK_DOWN );
// down_btn.setPreferredSize( btn_dim );
down_btn.addActionListener( new ActionVportDown( y_scrollbar ) );
super.add( down_btn );
super.addSeparator( mini_separator_size );
icon_URL = getURL( Const.IMG_PATH + "Edit24.gif" );