Is anyone able to help me with an unusual problem?

My template is embedding HTML from a remote content engine that I can't control, and I would like to change the size of an image. The only img size definition is width="450" and I would like it to display at 100%. I have been able to do this with CSS in the <head> for most everything except Outlook, and unfortunately getting the embedded code changed is out of the question. I've tried.

Is there a way to overwrite the HTML width with CSS for Outlook? Thanks for any help!

My Template:
.embed1 img {width: 100% !important; height: auto !important;max-width: 100% !important;}

<body>table>tr>td class="embed1">

Embedded Content:
img style="" src="image.jpg" width="450" height="">