Pictures not centered

When I click on the first image in a gallery it’s centered, but the next image drops to the bottom of the screen and only half is visible. Is there a way to fix this?

I read a suggestion in the WP support forum about editing the style sheet, but I’m not experienced with style sheets and figure I’ll break something (smile). My WordPress and NextGen are up to date and I haven’t done anything out of the ordinary. Is this just standard for galleries?

https://marianneconnolly.com/?page_id=26&show=gallery

https://www.ads-software.com/extend/plugins/nextgen-gallery/