Search for minimal in the obsidian theme browser (https://github.com/kepano/obsidian-minimal) and get it. It is also recommended using the hider plugin and the minimal theme settings.
Use the hider plugin to hide the title bar and app ribbon.
You can further customize the look by editing the css file of the theme
these are the default color values for the minimal theme
use these for Nord colors
use these for Gruvbox colors