Hey @jwillk, we’re working on adding that to the UI, but in the meantime you can add it to the custom code section as you have. Except you need to specify a tag-based selector, like so:
body { ... } ← Selects the entire document body and cascades the font setting to all elements on the page, which is what you want 
And not a class-based selector like you have in the above snippet:
.body { ... } ← Selects all elements with the class ‘body’, which is probably not what you want 
If you remove the period, can you see that change in the inspector? Let me know if it still doesn’t show up.