Q:

Set IMG.width to resize to container (DIV, etc.) width without .js

Is there a way to have an IMG resize it's width (and height to maintain aspect ratio) relative to the containing DIV?
Use Case
This is for an email newsletter, so I can't use .js  There is a containing div that resizes based on the page width. I want the IMG in it to "obey" that.
I've tried just setting Style="Width:100%" but that doesn't work.

A:

img {
    max-width:100%;
    height:auto;
}

Setting the height to auto is only necessary if a width and height attribute were set in the image tag.
http://jsfiddle.net/e2003kac/1/

