I have an editable combobox, where I need the left margin increased. I found the TextBoxStyle property and tried to use it, but it does not work. To ensure that I was doing things correctly, I tried setting other properties, such as the background, which do work. So I know that my style is being applied, but your ComboBox code is overriding it somehow.
I've worked around the problem by finding the textbox by it's "PART_EditableTextBox" name and manually adjusting the margin, but it is not ideal on several levels. If I am doing something wrong, please let me know what I can do differently.