How to add aria label to ext JS close messageBox

Question

Ext.Msg.show({
title:'Save Changes?',
message: 'You are closing a tab that has unsaved changes. Would you like to save your   changes?',
buttons: Ext.Msg.YESNOCANCEL,
icon: Ext.Msg.QUESTION,
fn: function(btn) {
    if (btn === 'yes') {
        console.log('Yes pressed');
    } else if (btn === 'no') {
        console.log('No pressed');
    } else {
        console.log('Cancel pressed');
    }
}
});

How do I add aria-label "close dialog" to the close icon at the top?

I am unable to add afterRender or listeners

Version: 3.4