field css and attributes do not work at all, at least not in the free version I just installed for testing.
inspecting shows this:
<button class="nui button colored " name="button_2" value="" id="button_2" type="submit" data-test="test"> Button 2</button>
view source, shows this:
<button class="nui button colored " name="button_2" value="" id="button_2" type="submit" data-test="test" class="test">
I'd like to harness the site style, not to use nui styles.
the Field Class is for changing the container div, so that will not update the input tag itself
The HTML Attributes class will always add a new attribute and so will not update the existing class attribute for a button, I think that you better do this for a button:
button[data-test]{
padding:10px;
}