Responsive image with slide box

I want to create slide box functionality in tabs. I done with demo. but the image which i want to show as slide image is not looking good in phones and tablets .
I used this code within img tag.
background-size:100% 100%;
I used a lots of css codes as well which are used to create responsive image.But cant get proper results.
Any help will be highly appreciated.

what about using class=“img-responsive”