It's not even :has, it's just how child selectors in CSS have always worked.

    // Not actually needed, here
    // for competition
    .group {}

    // Child selector
    .group:hover group\/hover\:bg-black {
      background-color: black; 
    }

    // Which is essentially the same as
    .group:hover child {
      background-color: black; 
    }