Thumbnail in 1.7 is not retina ready

[cpuin]

I have installed Prestashop 1.7.2 and I was surprised that it has built in option for generating High definition images.

Soon I was disappointed viewing the images on my Mac with Retina display.The main images and product images are OK, but the thumbnail is displayed blurry.

In cases that this option does't work properly I need one option, I want to set the size of thumbnail to 500px (instead of 250px) and displayed it in half of the size.Unfortunately I can't find the right css tag I have to modify.

If somebody have some suggestions how to solve this and whether there is an option to generate really High definition thumbnail, please, help.