Resizing images on mobile

Site URL: https://alligator-avocado-rmk6.squarespace.com/config/

Hello, 

Please could someone help me with the code to make the images on my testimonial sections smaller on mobile devices

There is a section at the bottom of homepage and on the services page. I have attached an image as an example. 

password: help12345

Thank you!

Add to Home > Design > Custom CSS

@media screen and (max-width:640px) {
div#block-yui_3_17_2_1_1590245630619_13759+.row>.span-2 {
    width: 50% !important;
    margin: 0 auto;
}
}