I don’t like paper-like background of OS X Notes.app, and the fact that, usually after syncing with its iOS counterpart, the application doesn’t remember the larger font size which I’ve set. Here’s how I fixed it to my satisfaction.

First, navigate to /Applications and Control+click on the Notes.app icon. In contextual menu, select the Show Package Contents item. Then, browse the content of the app’s package to Resources, and inside that find these two files: pad.css and paper.tiff. Make a backup copy of these files in a safe place in case you want to revert back to them sometime; otherwise you’d have to reinstall OS X to do so.

Copy the former into a folder you have write permission for, and open it with any text editor. Just replace the @[FONT_SIZE] on fifteenth line with whatever font size suits you. I’ve bad eyes and have choosen 18px. Save the file and replace the original with this modified version.

Th …

Source: Mac OSX Hints