I've worked on a text input that is now working nicely.
As you can see I implemented it in a save screen which now saves the current level on disk with the entered name.

Now to update the loading screen with the newest level data...

I also thought about how to implement a system to ensure only 1 GUI screen is active at a time. I don't want to be able to open 10 different screens on top of one another.
Currently the GUI screens are set up in a way where sub dialogs or other GUI elements are drawn depending on their parent screen.
So I'm thinking if I implement a rule where always 1 base screen can be active, then I won't disable myself of having subdialogs on top of base screens, which is good.

I'm really happy with the progress so far! Just a little more work and then the basic level editor is done! That will really speed up level making.
I'm still doubting on what to pick up after this part. Maybe replacing some placeholder UI graphics...