Zoom on product's images autosized

[Gohanki]

Hi!

I'm using Prestashop v1.7.6.5  with theme 'classic' and all the default modules.

I configured the images size 1800x1800 for the products and it's adjusted depending on the witdh.

On the product's page, when clicking on the image for zoom, the image size is 1800*xyz as I wanted. great! But it's bigger than my screen! I So I see only a part of the image  and the thumbnails for the other images are out of my screen.

<img class="js-modal-product-cover product-cover-modal" width="1800" src="http://shop.abc.com/31-large_default/myproduct.jpg" alt="" title="" itemprop="image">

Could it be possible to modify the CSS in order to have the image autosized in the popup ? 
I would like to keep a high resolution for people having a big screen or for people who want to save the picture on the computer.

Any help ?

Thank you!