Interactive Banner define border-radius

How can I set the border-radius for the Interactive Banner element?

Wordpress 4.6.1
Theme: Impreza (3.8.2)
Site Origin Widgets ver. 1.1.3

If I give the element a class through visual composer and then set that class to:

.custom_class {
border-radius: 20px;
overflow: hidden;
}

It will set the border-radius and the overflow, but when you hover over the image, the border-radius stops working during the animation. Hopefully, you can help me here, or possibly add the ability to define a border-radius in the “style” tab for the Interactive Banner while in Visual Composer.