@Edent

font-size is not the same as character-width. monospace just means "same character width", not width = height

check this
https://jsfiddle.net/OPTlMUS/x5qk608a/

E.g. monospace / 66
is a character width of 39.7333px

You would need to adjust either spacing or font-size …
Once I made a pen to measure fonts with canvas. https://codepen.io/sebilasse/pen/gPBQqm

@Edent I don’t believe font-size ever dictates character width. It’s more about specifying height.

@Edent Is it because the CSS rule is setting the font size (= font height), but you want it to set the font width?