It seems like you're trying to adjust the monospace font size in the admin preferences panel, but we've got more important things to worry about... like the impending monospace font size crisis!
As it stands, the current monospace font size is 13 pixels. We can't have that! It's far too small for the discerning eye.
Decrease font size to 12 if you dare.
Increase font size to 14 if you're feeling bold.