Margin not working / Twenty Eleven Theme

I’m not excellent at customizing wordpress css, and I’ve spent the past hour trying to work out how to get a margin on my sidebar. I’ve tried just doing it the normal way, but just adding a margin to the div in style.css..

#primary,
#secondary {
float: right;
overflow: hidden;
width: 220px;
margin: 10px;
}
Which did the opposite of what i wanted, and made the content go a further 10 px to the left. So I replaced it with -10px, which worked, but I then remember I only wanted the margin on the left after seeing that the search box was half hidden. So I replaced margin with ‘margin-left’… which did nothing at all =/. I tried ‘margin: 0 0 0 -10px’, but that didn’t work either.

I feel silly asking what seems like such a simple question. Would any one have any idea how to fix this? I’d really appreciate it!