Thank you for all your reply.
It’s ok for point 2 and 3 thanks to your help.
Even if I don’t know which is the size of the picures in sliders?
But I still cannot solve the first issue, even with your code below.
I tried also change the size of the image but nothing change.
I don’t know what is going wrong? I have also the same blog on Polish and it don’t work also.
Thanks for your help.