UX: Inverse colour for letters from built-in keyboard, improve readability.

[ghost]

Describe the bug Inverse colour for letters from built-in keyboard. Improve contrast (for both light and dark theme)

1. [Black theme] Font should be black and button should be white for remaining letters.

2. [White theme] Font should be white and button should be black for remaining letters.

3. Convert all letters to bold uppercase

4. Same for word's strip line

To Reproduce Steps to reproduce the behavior:

1. Open application
2. Switch to light / dark theme
3. Logout from wallet
4. Go to import seed
5. Enter half of any word

Expected behavior Letters remaining should be high-contrasted

Screenshots