CSS : Hide just an image from the page

Hello,
I’m currently trying these codes : https://www.seo-alien.com/wordpress/csshtml-code-hide-text-images-videos-from-mobile-phone/

So this

<div class=”mobileHide”>Text/Image/Video That is NOT for Mobile</div>

And this on CSS :

<style type=”text/css”>
.mobileHide { display: inline;}
/* Smartphone Portrait and Landscape */
@media only screen
and (min-device-width : 320px)
and (max-device-width : 480px){ .mobileHide { display: none;}}
</style>

In order to check if the code works, I replace 480px by 4000px. The effects apply immediately on the page builder, but when I save the page nothing changes. It doesn’t work on desktop nor on mobile…
What can I do?

Thank you.