I suggest you don't rely on stylesheets but rather create the inline code by hand and uncheck the option: Add stylesheets. If you find this difficult install emogrifier module (not sure but you might need to install htmlmail as well) that converts the stylesheet code to inline code.

I did myself an inline coding.

You might encounter an issue with weird characters breaking your lines in the email body, I am courious if this happens to you too, if so let me know. I think I have the fix for that too.