Code for zoom hover on poster images

Site URL: https://caradeckers-interieur.squarespace.com/

On the website: https://caradeckers-interieur.squarespace.com/ 
password: Cara1234
Page 'Projecten'

I want to add a slight zoom when you hover over the images. These are poster images. 
I used the code below in Custom CSS, however it didn't work. 
.sqs-block-image .design-layout-poster img:hover {transform: scale(1.1);}

Important to know is that there is text on the images and the images link to another page. 

The only Custom CSS code I'm using at the moment is: footer a {text-decoration: none !important;}
So I don't think there is any interference. 

Does anybody have a solution for this? 

Thank you in advance!