You can also do this with any theme if you setup a CSS Snippet:
// This is the one that works for me
.markdown-source-view.mod-cm6 .cm-scroller {
font-family: monospace;
}
// You may also want to do this one
.markdown-source-view {
font-family: monospace;
}
Then reading view will use whatever font you've configured in the settings.
Goes to show how Adobe's whole schtick about subscriptions meaning they can put more money into improving their products is bullcrap. Resolve is hot on their heels.