I would like to add some black opacity over all product images on the category page. How does this work?
You need to override below phtml file first with your custom theme:
and add css with below less file for your customisation with design:
It may help you to resolve issue.
If issue resolve, please click on 'Kudos' & Accept as Solution!
Thanks for sharing. I found by acceditent another option. I added watermarks over the images with an opacity of 10%