Comments in marp have to be in html format, otherwise the text is rendered to the slide.
Global styling, is used in the "first" page, as seen above (slide-deck.md)
Comments are visible inside presenter view, and therefore can be used as notes for the presentation.
About the SVG-Symbol: (OpenAI logo), path to a resource is from the standpoint of the rendered document, which resides in: ./docs/index.html, ./assets/open_ai_logo.svg would be the wrong path because assets is not on the same directory level as the docs directory.
Local styling
Vertically split background in "cover" mode with even spacing.
Picture on the left side using 33% of the page.
A series of pictures with the same height on the right side requireing 60% of space. The position (side) only has to specified once.
Picture (qr-code) on the left "position" is not specified, so the picture is rendered in at the "foreground".
Blurred picture as a background. Pictures from the internet can also be used.