ExtJS 4.2.0 - Ugly and wide checkbox column

I have a grid panel (Ext.grid.Panel), with selType as "checkboxmodel". I am NOT adding any specific checkbox column myself.

When the grid is rendered, it does show the checkbox column as the first column automatically, but it is ugly and wide

How do I make it lean and pretty just like it shows in the ExtJS Grid plugins examples? My code is pretty much same as those examples.

Here is how it looks:

Capture.JPG

And here is how I want it to look:

2Capture.JPG

Thank you for your help!

ExtJS 4.2.0 - Ugly and wide checkbox column