Thank you for the donation! I hope you get good use out of the system :)
For your first question - you can provide the description to the hide_description property. See hidden_double_unlock for an example of this, though if you want the name to show, you won't also include hidden=True (which would show the name as ???). So it would probably look like hide_description=_("This achievement is hidden.") or similar.
Second question - if you hover over the text in question and hit shift+i, you'll see the styles applied to it. I don't use custom gui values for styling, so you can just directly specify the font on the screens themselves or in the styles the screens are using. By default it'll just use the font for your project.
Third question - you are welcome to adapt it to use that! You should keep the popup screen declaration provided in this code - i.e. the name of the screen + the arguments, and keep the timer at the bottom, but the styling itself can be copied over and the popup ATL transform adjusted to suit another popup animation. That's something that's out of the scope for me to help with here, though I may consider integrating the two better down the line.
Lastly - you can grab the system files from GitHub or itch.io; they both have the same code. I've updated both with a few fixes and updated features after release, with the last being about two months ago, so if you downloaded it earlier than that, you can check the devlog notes for what changed.
I hope you have a great new year also!