TextBox is a GWT widget, whereas TextField is a GXT one, so the styles that apply to TextBox aren't going to automatically change TextField or vice versa.
Without reset.css, a variety of style problems are going to arise - you cannot simply replace GXT's reset.css with GWT's Clean theme - again, GWT styling doesnt do anything for GXT. The reset.css file isn't really optional for the default GXT Blue and Gray themes - without it, there are several bugs that will occur.
Neil's blog post is more about how to switch appearances, or even to build your own - this is useful to totally reskin widgets or cells. Nowhere in that post does he use the three methods you are trying.
That said, what are you trying to do with your style?
is going to remove the style on the root element, but won't remove all the styles on other elements in the widget
is going to do nothing - it is adding an empty css class name
is going to update the primary and dependent names in the widget - this isn't a feature that GXT 3 uses, in favor of following the Appearance pattern to allow widgets and cells to be totally rethemeable.
If you want to add a new css class to a widget, addStyleName(String) is the simplest way to add it to the base of the widget:
results roughly in this structure:
TextField field = new TextField();
So the tools seem to work to set up styles, but what are you trying to achieve? I'm sorry to hear you are frustrated, but we need more to work on to try to help you...
style="width: 150px; position: relative;">
<div class="GKJJX3KBFY" style="width:150px;">
<input type="text" class="GKJJX3KBEY GKJJX3KBPX"