The article diagrams can’t be seen well if the device has the dark mode as default, just a suggestion for the author.
Opened with Safari in iOS
I have the same in Brave on iOS: to see the the diagrams I need to turn of Night Mode.
I only saw one diagram but it is perfectly visible for me on the desktop.
The page appears to be dark themed even without dark mode enabled; if I use Noir to force-add dark mode, then the diagrams indeed become difficult to read but this seems like a Noir issue more than a site issue