How did they get the exact effect to show what they want in the text here instead of say, me seeing the exact same visuals for each browser as I am reading it from a single browser?
You mean in the parts that say "Here's what they look like in Safari" and so on? Those are just .pngs.
I missed some UI improvement in browsers then as I can copy and paste them as text, and even the italic emoji example carried over the italic information when I tried copying it into various editors.