I generally agree and wince at anything deeply nested, but there's no question that the biggest benefit here by far will be pseudoclasses. Especially when you wanna do something to children elements based on a pseudoclass

  .page form
    border: 2px solid #223;
    border-radius: 0.15rem;

    & button {
      background-color: red;
      transition: background-color 0.15s ease;
    }

    &:hover button {
      background-color: blue;
    }
  }

seems way cleaner, easier to read, and more maintainable than the alternative which I don't even wanna type out