Featured image still available after hiding it with code

Hi guys,
I have italian and spanish site.

This code is supposed to hide the featured image.
/* Hide featured image from blog post */
.post-entry .big-preview {
display: none !important;
}

However it works on the italian side but not on the spanish site.

You can see 2 features images on this spanish site. The one added manually (correct) and the on (the toppest one which should be hidden via code)

Can you please help?

Thanks,
Marco