Is there a default size for an image when using the Percussion Image widget for it to be responsive?

Trying to use Percussion CM1 Image Widget, says its responsive. However when I add an image to the widget it is the original size (1300wide) and is not responsive. Is there a default size that is required to use? Is this widget even responsive? 

Do you have a live page for example? I have like 1300px width and it is responsive. Make sure your CSS setting is this:

img {
    max-width: 100%;
    height: auto;
    display: block;
    margin-left: auto;
    margin-right: auto;

Thanks! I assumed the CSS was already established by percussion since they supply an image widget marked as responsive. 

I don’t know about that. I usually stripped out entire Percussion’s css (making it barebone css) and integrate with my own css.