feat: improve overlay style

[assynour]

Improvements:

• increase the font size of the overlays
• use the same color for stroke and fill
• use a more visible font color when possible: white or a different black flavor

closes #54

[github-actions[bot]]

:recycle: PR Preview a7053223646a6ab5de829c7abbbe8e941c7fa37c has been successfully destroyed since this PR has been closed.

_{🤖 By surge-preview}

[csouchet]

I changed the font color of the overlay labels:

@tbouffard What do you think ?