Could you tell me what is the namespace of s:fileUpload? Is it a RichFaces or a Seam tag?
Its's a seam tag.
1) I'm afraid that you should better raise this question on the Seam form.
2) I managed to find that s:fileUpload has these two attributes. Do they match your requirements ?
- style — The control's style
- styleClass — The control's style class
3) You can try to play this styles of this tag if FireBug. So may me you can override them in your css and it will work for you.
I tried with those and lots more and I didn't get any answer on Seam form about this question yet. But i notic that many developer had a same problem.