如何格式化bootstrap表单标签以匹配表单输入的宽度？

<form>
  <div class="row">
    <div class="col-md-6">
      <div class="form-group">
        <label class="col-form-label">姓名</label>
        <input type="text" class="form-control" placeholder="请输入姓名">
      </div>
    </div>
    <div class="col-md-6">
      <div class="form-group">
        <label class="col-form-label">邮箱</label>
        <input type="email" class="form-control" placeholder="请输入邮箱">
      </div>
    </div>
  </div>
  <div class="row">
    <div class="col-md-12">
      <div class="form-group">
        <label class="col-form-label">消息</label>
        <textarea class="form-control" rows="3" placeholder="请输入消息"></textarea>
      </div>
    </div>
  </div>
  <button type="submit" class="btn btn-primary">提交</button>
</form>