Sublime text doesn't recognize the calc() as function

Question

I have the following css code:

div {
  --height: 1.5em;
  line-height: var(--height);
  background-image: repeating-linear-gradient(transparent 0 var(--height), green var(--height) calc(var(--height) * 2));
}

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This css code does work well, but I am not sure why, the sublime text don't recognize the calc() as a built-in function.

It does display properly even though the sublime text doesn't recognize the calc(), but could anyone explain to me a little bit why this happens?

It looks something like this:

Thanks for any responds!