There is nothing built in, however you could try set the theme to "Dark" and then add these your custom CSS, both for rendered Markdown and Joplin itself (see Options → General → Appearance → Show Advanced Settings).
:root {
--joplin-background-color: black !important;
--joplin-color: white !important;
}
Restart the application to see the effect. Of course, more tweaking will be necessary to make everything use higher contrast, but it's at least something.
