I am not familiar with the concept of @extend. Is it what we should have?

%olPopupMargin {
  margin: 5px;
}

.olPopup h1, .olPopup h2, .olPopup h3, .olPopup h4, .olPopup h5, .olPopup h6, .olPopup p, .olPopup ol, .olPopup ul {
  @extend %olPopupMargin;
}