Set css Padding 0px 0px 0px 0px pixel on select field

Setting the padding in the advanced edit of the css (forms / simple record / object) I reduce the space between the text and the border of the text field.
I can’t do the same thing with a select field, the text is always about 3 pixels from the edge which I can’t reduce.
Any suggestions?
TKS

Did you clear your cache after you changed your setting?

Yes
if you try to change the padding (on the left) in any theme you will see in the preview that the text (xxxxxx) in the “text” fields moves by attaching itself to the border but in the select field it remains about 3 pixels apart ( Afghanistan)