Except it seems that they are defined in code[0], calling FLTK functions (these draw_xxx functions are wrappers/bindings for Fl_xxx functions). I'm not sure where exactly things break, the code (at least the linked one) seems mostly straightforward. Does FLTK try to scale draw call coordinates? While scaling coordinates is helpful in general, for low level drawing like implementing themes, it should be disabled and have the themes handle scaling themselves in a way that doesn't look like someone applied widths and heights randomly.
I wonder if this is an FLTK limitation or the theme author not paying much attention to details.
[0] https://github.com/fltk-rs/fltk-theme/blob/main/src/widget_t...
I am very curious what you mean by this, because they look fine to me.
The author of these themes replied a couple of hours ago and he mentioned that indeed it is due to scaling. Compare the image he posted[0] in how the themes were supposed to look with how the images look in the screenshot i replied to and you'll see the issue.