How to Adjust Responsive Settings for Feature Images

Hi, I am using a child theme of Zerif Lite at new.healthcatalystcaptial.com and I’m trying to figure out how to adjust the responsive settings of feature images on mobile devices. The feature image is full width, but I’d like only a portion of the image to be shown when shrunk down to mobile size so that the height can remain intact. To make this happen, I am currently using a responsive slider plugin (Slider Revolution) and it works well, but for my Team page, the plugin conflicts with another gallery plugin that I am using. Therefore, I’m trying to go back to the feature image instead and adjust the responsive settings in css, but I can’t figure out how to do so. I tried adjusting the post.image width settings but that didn’t work. Any ideas??