[SOLVED] Widget Content Box?

Hi,

I'm trying to change the text-widgets margin, but when I input "margin: 0px 7px 0px 7px;" in the Widget Content Box under Style Widgets, nothing happens.

I don't understand. Why doesn't it work? If I should do it manually in the CSS, please tell me exactly what to type, I'm not too familiar with CSS.

Thanks in advance!