Why this code donot execute flipping?

Question

I tried to flip but it donot work.Tell me the solution to do it.I am attaching code for reference.
https://code.sololearn.com/W2Iu5FLrvNKz/?ref=app

Answer 1

line 19 :
.flipcard:hover .flipcard-inner{

line 36:
transform : rotateX(180deg);

Answer 2

Also set the perspective around 1000px for better result.

Answer 3

https://code.sololearn.com/WDr2gkUpbG7p/?ref=app

Answer 4

Things to remove:
.flipcard-inner
Things to add:
perspective: 2000px
Things to replace:
rotateX (180deg) => rotateY(180deg)

Answer 5

https://code.sololearn.com/W2Iu5FLrvNKz/?ref=app