The text will have a white background, but only where there’s text the rest of the document will keep its dark background making the whole thing difficult to read (and terrible looking.) Unfortunately if you use Notepad++ with a dark-mode type of theme (light text on dark background) the way Notepad++ highlights Markdown hurts more than it helps. And it can assist skimming large marked down documents. Nevertheless some coloring can help to spot errors such as accidentally indented blocks of text or badly formed lists. Markdown on its own tries to look readable and doesn’t need extensive syntax coloring or highlighting. It also explains how to get the highlighting to work better / differently for different mark-down flavors.

Update: Here is a repo I discovered after writing this post with pre-defined dark themes.

You have to manually edit a special Markdown theme to change most of the colors and fonts. This is especially apparent when using a dark-mode Notepad++ style and dark theme in Windows. Changing the default Notepad++ theme doesn’t change most of the colors in a Markdown document.

Notepad + + dark mode