Featured images don't display on mobile

Hey there,
I’m trying to fix this issue without success…
The featured images don’t display in the blog feed and the single posts on mobile.
They display on tablets.
I’ve added the following media query in screen.css but it hasn’t solved the point.
@media (max-width: 500px) {

*.post-card-image {*

*width: 100px;*



AMP is enabled but the issue occurs even when it’s disabled.

The URL is: https://www.cryptodidacte.fr/
Latest Ghost version.
The theme is based on Casper.

Could anyone give me some help to fix it?