Provide more flexible image scaling or styling

On my wagn, there are some pages where I'd like to include images that are as large as they can comfortably be -- that is, the width should be scaled to the size of the content div, rather than be a static number like "small" or "medium" or "large" (or even "original", since the size of the content div might differ depending on the browser resolution).

The Image card here suggests putting styling directives directly in the inclusion tag, so I tried doing that (i.e., I put "width:100%;height:auto;" in the Image inclusion tag; but that doesn't help, because it puts the style attribute on the div that contains the image, rather than on the image tag itself.

It would be nice if there were a good way to add a style attribute to image tags in the rendered page. (For my immediate purpose, I'm just adding a new "fullwidth" view that can be used for Image cards; I have no idea if that's a good way of doing it in general.)