This is my best "first draft" code on this... I already spent too much time on it so hopefully it'll get you going in the right direction:
.rokbox-container.rokbox-type-image, .rokbox-content, .rokbox-content img {
max-width: 100% !important;
max-height: 100% !important;
width: 100% !important;
height: 100% !important;
}
This is how to create a custom CSS override file compatible with Gantry 4...
Simply create a file called "<TEMPLATENAME>-custom.css" and put this file in the CSS folder of the template (where <TEMPLATENAME> is the name of the template as seen in template manager e.g."gantry"). GANTRY4 will automatically load this CSS file. If you wish, you can also have browser specific files by appending, for example, "-ie9" making the filename "<TEMPLATENAME>-custom-ie9.css"
More here:
www.gantry-framework.org/documentation/j...custom_stylesheet.md
Even more here:
www.rockettheme.com/forum/free-joomla-st...-or-less-custom-file