message: Add message to user about empty groups when validating the demo
diff: .ruleGroup.queryBuilder-invalid .ruleGroup-addRule {
  font-weight: bold !important;
  }
  +
  + // Purple outline for empty text fields
  .rule.queryBuilder-invalid .rule-value {
  border: 2px solid rebeccapurple;
  }
  +
  + // Message to user about empty groups
  + .ruleGroup.queryBuilder-invalid > .ruleGroup-body::before {
  + content: 'Empty groups are considered invalid. Avoid them by using addRuleToNewGroups.';
  + }
  }
  // all styles except for default
  