In our NG Client we attach a toolTipText to a TEXT_FIELD. It does not display in the browser. It works for a field of displayType IMAGE_MEDIA. But according to the documentation it should also work for a text field.
The tooltip property is supported for the TEXT_FIELD element in the default components.
It can be related to a css setting what is blocking the tooltip to display correctly.
I gave it another try, looking for a css definition, blocking the tooltip (as I understood your post).
css seems not to be the problem. But I found, that the text field must be set to editable to raise a tooltip. Since my field is never editable, I made it a label. Now, the tooltip works as expected.
Thank you again, I was glad to get another answer to my question.
Kind regards