How to have a panel take up the whole page?

How would I modify this snippet from the tutorial

Ext.get(document.body).update('<div id="test"></div>');
new Ext.Panel({
    renderTo: 'test',
    width: '200px',
    t开发者_运维技巧itle: 'My Title',
    html: 'My HTML content',
});

so that the example panel took up all available space?

new Ext.Viewport({
    layout: 'fit',
    items: [{
        title: 'My Title',
        html: 'My HTML content'
    }]
});