Bug: Expanded icon and collapse icon don't change the visual

I've made a theme and everything works fine, but the expanded icon and collapsed icon just haven't changed. I've inserted it with all the other icons in themes.ini. Also, I changed the images of pre-existing themes and even doing that they don't show the new images, but only the default for these two icons.

I'm using Linux Mint 21.2 with NixNote2 version 2.1.6+dfsg1-1

THANKS!