ui: make code and input text fields monospaced

[xyzshantaram]

This makes it a lot easier to write code. I might also try and add a version of the Ace editor to this and define a custom syntax highlighting rule, but that's for later.

This is my first time working with Vue, apologies if I did something that is a no-no.

Edit: The package-lock.json file rebuilt itself when I did npm install, not sure what to do about that except let it be.