Hello! ext:TextField is meant to be one line high. The component having several lines and supporting line breaks would be an ext:TextArea.
Otherwise, if you really want to fiddle with the textfield, you can:
- change it via CSS, either creating a CSS class and binding it to the field with Cls="className",
- just inspect the textfield's DOM with your browser's debugging tools and get which classes you want to override (and, of course do override them for your liking)
- inline-specify CSS classes with StyleSpec
As for text field height, you'll probably want toget the textField's inputEl DOM component and style it.
Hope that helps!