Have you gone to display settings and enabled the "large code font" option? That actually removes an instance of "<font size='-1'>" that gets wrapped around each code block by default.
One day that should go away as well. Those who don't like the "same size" code that appears "bigger" (because fixed-width fonts end up being noticeably wider) can adjust such using custom CSS rather than a user option implemented using old-school font resizing tags.
Similarly, those who like reply text being a notch smaller (as has long been the case) should feel free to add their own CSS to make that happen (after the proposed change). I'm not in favor of adding CSS to try to emulate the current <font size='-1'> because I don't believe CSS can fully emulate that across all environments. Certainly, it will be easy for individual users to pick precisely the font size they desire with custom CSS.
So we should document how to update custom CSS to get something that is likely to be similar to the old rendering for most situations and that can easily be adjusted by people. Perhaps the following is close to such:
If that isn't close, please propose something closer for others to iterate. Though perhaps a new div and class are in order here?
In reply to Re^2: Size of text in replies when showing threads (options)