set the buttons at the bottom and yet full stretched in width in sencha touch

set the buttons at the bottom and yet full stretched in width in sencha touch

i am trying to align button vertically and then want to set it to the
bottom of the screen but as soon as i set its property bottom:0 buttons go
down but they dont stretched full in width.
wht i want is i want to set it to bottom and fullscreen in width.

here is my code
Ext.define("ca.view.cav",{
extend:'Ext.Container',
xtype:'cv',
requires:['Ext.Button','Ext.Panel'],
config:{
bottom:0,
defaults: {
margin: '10 0 0 0'
} ,
items:[{
xtype:'button',
text:'YES'
},{
xtype:'button',
text:'NO'
},{
xtype:'button',
text:'PROBABLY YES'
},{
xtype:'button',
text:'PROBABLY NO'
},{
xtype:'button',
text:'DON\'T KNOW'
},{
xtype:'button',
text:'SKIP'
}]
}
});
and i am adding this container in to other panel as xtype:cv