Make gallery full page size on all browser

Site URL: https://espace-one.squarespace.com/

Hi, I would like to customise the gallery on my homepage: https://espace-one.squarespace.com/ (password is "design") so that it always takes 100% of the width of the page. Right now, the image is too high for my browser, while on other browsers, it is too small. I always want it to take 100% of the page, so there is no scroll going on on the page. It seems to be a simple function, but I can't seem to figure it out..