vistered little image margins

I want to get margins around my images in “vistered little” without having to edit the code each time, which I should be able to accomplish using the img tag in the css, however it doesn’t work.
I am able to use .post img {margin: 5px; } successfully in other themes, but this same principle doesn’t appear to work in “vistered little”, seems I have to manually apply a class to the image each time using something like .imgmargin {margin: 5px;}.
Even the img button in the text editor can’t get it to respond to horizontal and vertical space values.
Can anyone tell me how to get margins to appear automatically for images when they’re added in the “vistered little” theme ?

P.S.
I’ve tried applying the css in ALL the accompanying stylesheets …