I call attention to this passage from the next version of the Help file at For Advanced Users > Customizing NoteCase Pro > .ini File Hacks > Change Toolbar Button Sizes.
To change the size of the Toolbar buttons, you can edit the notecase_pro.ini configuration file and add line "ToolBarButtonSize=1" under "[Display]" section (valid sizes from 0 to 3, smallest to largest).
See .ini File Hacks for instructions to edit that file.
Note that this only changes the size of GTK stock icons. It will not change the size of all icons available through the Icon Picker dialog.
[curse omitted] I have struggled with NC Pro since returning to the Linux Mint with Mate desktop. Some of the toolbar icons are near-transparent. In particular, the history back and forward icons all but disappeared.
But after using this hack with its value set to 2, I am going to get along much better with the result than pre-result.
-- [Notice not included in the above original message: The U.S. National Security Agency neither confirms nor denies that it intercepted this message.]
¯\_(ツ)_/¯