Steven Zahm@ Christine
This very, very likely a caching issue… just about always is.
If the theme has a cache, clear it.
If you are using a page caching plugin, flush your page cache.
If you are using server page caching, flush the cache.
Force refresh your browsers.
What is the folder and file name?
You said you placed the folder/file in several locations. Did you put them in all locations or simply move them from one folder to another? You only need to have it in the child theme or one of the others.
The only thing I can say for certain… the css I gave is not being applied, even even loaded.
Oh… just noticed that the /themes/Divi-Child/connections-templates/excerpt-plus/excerpt-plus-custom.css file is being loaded so that is just fine. But, the CSS I gave you, it is not in the file. I suggest checking the file and making sure it there. I suspect you made the change, it got cached on your laptop, but then somehow reverted so you see the cached version while everyone else is seeing the version without the white CSS statement.
Hope that helps!