Issues with updated theme

Hi,
I am working on a site for a friend. She contacted me because when she tried to make a new gallery the first image of the post wouldn’t show up…I thought maybe the issue was an incompatibility between her theme version and WordPress so I updated her theme to the most recent version.

However now when you choose a gallery the page background color is lost, and when you click on a thumbnail of an image it appears for a minute and then the page goes completely white. And the initial issue that when you create a new gallery no images are visible remains.

The site is https://lauriedanial.com/.

Thanks Kindly for your help,
Zoe