SPC T s in Spacemacs will allow you to scroll through the list if themes and see what they look like

As the page mentioned is markdown text and not an Emacs screenshot, then you could try search for the theme used by GitHub for code blocks

Yes it looks like they are using PrettyLights so I wasn't looking at a theme after all 😅

I guess you meant the page and not the portal screenshot on that page? The screenshot looks like Nord

No, I actually was referring to the screen shot, I like the theme but it was not a screen shot, just markup with syntax highlighting. But I like the nord theme too