Keyboard on the notebook. Dark letters, difficult to recognize?

Does anyone know of your ability to illuminate the letters on the keyboard so that they are easier to recognize.

Illuminated keyboard is clear, I know. But not an option because installation is too expensive.

Is there anything that can be put on the individual letters, characters of the keyboard, to improve the contrast and increase the visibility.

It would be simple:

https://www.google.com/...irefox-b-d