Colored blurred background on web browser version

When I click on the eyeball icon to preview the story on different devices, there is an “Open Story” button in the top right corner. I assume this is the web browser version of the story. I noticed that there is a colored, blurred background. The colors and blur pattern are different on each slide, and seem to mimic the color of the video or artwork.

What is creating these different backgrounds, and is there a way to remove them, or make them all the same color? Thanks in advance.

The page I need help with: [log in to see the link]