How can I modify input variables with string modifiers in zsh?

I've been working on a bold function as a proof-of-concept and a challenge to myself. I am trying to input text (e.g.foo) and have it print to standard output as it's bold counterpart (**foo**). Context: I've been using echo and basing it off of my PROMPT variable in my theme file. I am not using any frameworks. The theme uses codes like %B%n%b to bold the username (%n), but I don't know how to replace that %n with user input ($1). Any Help? Edit: Attempted Code

echo '%B'"$1"'%b'

-tried with and without quotes in various locations, as well as with sub-shell ({})