Jetpack slideshow background not consistent

I’m using the slideshow function that comes with Jetpack and I want a white background so I’ve added this to the CSS in my theme.

.slideshow-window {
    background-color: #ffffff;
    border-color: #ffffff;
}

On some pages it works and on others it doesn’t.
I’ve also set the media settings to a white background.

https://www.theaterbutton.com/show/about-the-show/ has a black background
https://www.theaterbutton.com/illustrations/ has a white background

what have I done wrong? Any ideas appreciated!