Kivy's stock disabled button texture is pale at the edges and dark in the
middle. Stretched across a wide button the edges stay put and the middle
grows, so it reads as three vertical bands with the label sitting on the
dark one and disappearing - "Delete dump" is unreadable at startup, where
it is disabled because no dump is loaded yet.
Keep the normal background for the disabled state and let the dimmed label
carry it instead. The text goes to 45% rather than Kivy's 30%, which is
faint on that grey.
Applied as a Button rule because nine buttons across the app bind
disabled: Export, Open folder, the camera button, Samples, the bin button
and the rest all band the same way. The one button that sets its own
transparent background stays transparent, since background_color
multiplies the texture.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
