When using a partial shorthand for the animation property, lightningcss replaces the value with none.

Expected behavior, the following is unmodified:

.foo {
  animation: infinite;
}

Actual behavior, the property value becomes "none":

.foo {
  animation: none;
}

When all properties are specified it behaves correctly:

.foo {
  animation: 3s ease-in 1s infinite reverse both running slidein;
}

Link to playground