const Header = styled.div`
  ${something()}
  & > ${Child}:not(:first-child) {
    margin-left: 5px;
  }
`;

const Header2 = styled.div`
  ${something()}
  & > ${Child}${Child2}:not(:first-child) {
    margin-left: 5px;
  }
`;

styled.div`
  ${foo}-idle {
  }
`;

styled.div`
  ${foo}-0-idle {
  }
`;

styled.div`
  font-family: "${a}", "${b}";
`;