I think the one on the website is just an abstract representation but one could replicate the look with the plugin Full House Template, here there is the related example: Shiny `Glass Card` from Logseq landing page · stdword/logseq13-full-house-plugin · Discussion #9 · GitHub
If you just want the icon of a page (it is set using the special icon:: property and specifying an emoji as value) there is a plugin, Awesome Links, that can display it next to page references. IIRC it also has a way to assign the same icon to a class of pages.
I don’t think namespaces are involved here.