Timeline Images not displaying on mobile?

Hi,
We are building a site for a client and have noticed that the imagery works fine on PC in the timeline, however on mobile it shrinks and is greyed out?
This seems very odd that it’s doing this????

We are also using this CSS to increase the as it makes it look a lot better
.avia-timeline .milestone_icon {
height: 120px !important;
width: 120px !important;
line-height: 120px !important;
}

We would like to make the images even bigger, however, in mobile testing, it things fall apart.

Thanks for your help in advance!

Craig