adding dark theme to Guess the Number app (neon)

[Palani-SN]

solves issue #76

• Added separate zones for the card placements (justified them to center)
• Added dark theme (neon) & toggle switch for theme control

Kindly review the changes, @mturoci

[Palani-SN]

Thanks @Palani-SN! A few comments from me.

I have made changes as per your inputs, Kindly have a look

[Palani-SN]

Thanks @Palani-SN, getting better, but still some room for improvement.

Sure, will make the required changes by today EOD,

Thank you,

[Palani-SN]

Thanks @Palani-SN, getting better, but still some room for improvement.

I've made the changes, as per your inputs, kindly have a look.