They are added. See LabelCustomClass and FieldCustomClass.

<div id="attrib-fields-0" class="tab-pane">
<div class="control-group">
			<div class="control-label"><label id="jform_com_fields_text-lbl" for="jform_com_fields_text" class="LabelCustomClass">
	Text</label>
</div>
		<div class="controls"><input type="text" name="jform[com_fields][text]" id="jform_com_fields_text"  value="" class="FieldCustomClass"              />
</div>
</div>

Oh they're added to the input, not to the main control-group. That's not very useful. It should really be added to the control-group to be able to style the field. Not much you can style when adding it to the input.

Please provide an example that you would you do that you can't do now as it.

A wrapping container (.control-group or .form-group with Bootstrap, .field with Semantic UI, etc. etc.) is really more of a framework specific design. To me it's right having the field class apply to the actual form field element (<input>, <select>, <textarea>) and not a wrapping container. And I'd be hesitant to suggest a param for a class on a wrapping container. Then again, the Bootstrap coupling is so real that maybe it isn't that terrible of a thing to force.

A similar issue here #11887

I agree with @AndySDH on this. True, if you rely completely on CSS frameworks then a class on the field itself has some benefit. For those that write their own CSS, a class on the parent .control-group gives you far greater scope in what can be achieved.

Please provide an example that you would you do that you can't do now as it.

Well it's very simple. With the current way, you can only style the input.

<input type="text" name="jform[com_fields][text]" id="jform_com_fields_text" class="FieldCustomClass" />

Instead, if the class was in the control-group:

<div class="control-group" class="FieldCustomClass">....</div>

You would be able to style the entire field output, give it a custom background, a custom border, or whatever else. And still also be able to style the input with .FieldCustomClass input

So I see no side effects in having the class in the control-group. It's kinda useless just in the input imho. Didn't even notice it was there and let me to believe it was broken.

From a user perspective, there is framework classes, they may wish to apply directly to a field which is the point @mbabker is making. It really depends on the type of user we expect with Joomla.

@AndySDH Is this still needed? Or we can live with what we are having now ?

I would say this is still needed. It would be a significant improvement and would allow to style individual fields in the form, which is not possible now.

OK. Thanks for your feedback. Hopefully someone will come up with a solution (I haven't spent enough time with custom fields yet, so I could not comment about it further)

Would a third field "wrapper class" could be a solution?