You need to specify the unit of your perspective [px
,em
,pt
,etc].
In your code, it should be:
transform: perspective(300px) rotateY(20deg);
Instead of:
transform: perspective(300) rotateY(20deg);
The number without a unit is meaningless and invalid according to the w3 docs, unless the value is 0
. (You can also refer to this SO answer
On another note, you should also have a non-prefixed @keyframes
, as most newer browsers support it.