How I can add all border with the help of CSS rule?

Question

https://sololearn.com/compiler-playground/WW94rRgtw88a/?ref=app

How I can add all border with the help of CSS rule?
And also want to center the table with this CSS rule.

Answer 1

Was wondering this too xD

Answer 2

Not working.

Answer 3

KnightBits Thank you so much. It solved.