Post image size

Hi,

I created a post, format is Gallery, added 3 images. The display size of the image is larger than the actual size. The issue was posted by another user in the comment section and I followed your reply and added this to the Quick css:

img.attachment-kleo-full-width {
width: auto;
}

But it still doesn’t work for me, the slider image is larger than the actual image. Help please.