How to align center?

Desktop
,
1 
this._indicator = new PanelMenu.Button(0.0, this.metadata.name, false);
var label = new St.Label({ text: '00:00\n1/1 一' });
label.set_style('text-align:center'); // useless
this._indicator.add_child(label);
Main.panel.addToStatusArea(this.uuid, this._indicator);