<div class="col-sm-11 text-center">
                    <div class="input-group">
      <span class="input-group-btn">
         <asp:Button runat="server" ID="btnCheck" CssClass="btn btn-default" Text="Sprawdz" OnClick="btnCheck_OnClick" />
      </span>
    <asp:TextBox runat="server" ID="tbNickName" CssClass="form-control"></asp:TextBox> <!----  <input type="text" class="form-control"> -->
    </div><!-- /input-group -->

            </div>