Hi Waghmare,
Refer the below code.
HTML
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="uc" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title></title>
    <style type="text/css">
        body
        {
            font-family: Arial;
            font-size: 10pt;
        }
        
        /*CSS Classes For Design Modal*/
        .modalPopup
        {
            min-height: 75px;
            position: fixed;
            z-index: 2000;
            padding: 0;
            background-color: #fff;
            border-radius: 6px;
            background-clip: padding-box;
            border: 1px solid rgba(0, 0, 0, 0.2);
            min-width: 290px;
            box-shadow: 0 5px 10px rgba(0, 0, 0, 0);
        }
        .modalBackground
        {
            position: fixed;
            top: 0;
            left: 0;
            background-color: #000;
            opacity: 0.5;
            z-index: 1800;
            min-height: 100%;
            width: 100%;
            overflow: hidden;
            filter: alpha(opacity=50);
            display: inline-block;
            z-index: 1000;
        }
    </style>
    <%-- Used links for References --%>
    <link media="screen" rel="stylesheet" href='http://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.0.3/css/bootstrap.min.css' />
    <link rel="stylesheet" type="text/css" href="https://cdnjs.cloudflare.com/ajax/libs/jquery-footable/0.1.0/css/footable.min.css" />
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
    <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/jquery-footable/0.1.0/js/footable.min.js"></script>
    <script type="text/javascript">
        /* Applied Responsive For Grid View using footable js*/
        $(function () {
            $('[id*=GridView1]').footable();
            var prm = Sys.WebForms.PageRequestManager.getInstance();
            if (prm != null) {
                prm.add_endRequest(function (sender, e) {
                    if (sender._postBackSettings.panelsToUpdate != null) {
                        $('[id*=GridView1]').footable();
                    }
                });
            };
        });    
    </script>
</head>
<body>
    <form id="form1" runat="server">
    <uc:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
    </uc:ToolkitScriptManager>
    <%--Grid With Add New Employee button Design --%>
    <asp:UpdatePanel ID="upgrid" runat="server">
        <ContentTemplate>
            <div align="center" style="padding-top: 20px;">
                <div class="row">
                    <div class="col-md-12">
                        <div class="form-group">
                            <div class="row">
                                <div class="col-md-12">
                                    <asp:GridView ID="GridView1" runat="server" CssClass="footable" AutoGenerateColumns="false"
                                        Style="max-width: 500px">
                                        <Columns>
                                            <asp:BoundField DataField="Id" HeaderText="Id" />
                                            <asp:BoundField DataField="Name" HeaderText="Name" />
                                            <asp:BoundField DataField="Country" HeaderText="Country" />
                                            <asp:BoundField DataField="Salary" HeaderText="Salary" DataFormatString="{0:N}" />
                                            <asp:TemplateField HeaderText="">
                                                <ItemTemplate>
                                                    <asp:Button ID="btnEdit" runat="server" Text="Edit" OnClick="Edit" CommandArgument='<%# Eval("Id") %>'
                                                        class="btn btn-primary" />
                                                </ItemTemplate>
                                            </asp:TemplateField>
                                            <asp:TemplateField HeaderText="">
                                                <ItemTemplate>
                                                    <asp:Button ID="btnDelete" runat="server" Text="Delete" OnClick="Delete" CommandArgument='<%# Eval("Id") %>'
                                                        class="btn btn-danger" />
                                                </ItemTemplate>
                                            </asp:TemplateField>
                                        </Columns>
                                        <EmptyDataTemplate>
                                            <table cellpadding="0" cellspacing="0" width="100%" class="footable">
                                                <tr style="background-color: #DCE9F9;">
                                                    <th class="hidden-xs">
                                                        <b>ID</b>
                                                    </th>
                                                    <th>
                                                        <b>Name</b>
                                                    </th>
                                                    <th class="hidden-xs">
                                                        <b>Country</b>
                                                    </th>
                                                    <th class="hidden-xs">
                                                        <b>Salary</b>
                                                    </th>
                                                    <th>
                                                         
                                                    </th>
                                                    <th>
                                                         
                                                    </th>
                                                </tr>
                                                <tr>
                                                    <td colspan="6" align="center" style="text-align: center;">
                                                        <b>No Records Found</b>
                                                    </td>
                                                </tr>
                                            </table>
                                        </EmptyDataTemplate>
                                    </asp:GridView>
                                </div>
                            </div>
                        </div>
                        <div class="form-group">
                            <div class="row">
                                <div class="col-md-12">
                                    <asp:Button ID="btnAdd" runat="server" Text="Add New Employee" OnClick="Add" class="btn btn-success" />
                                </div>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
            <%--lnkFake Link Button for mpeAddUpdateEmployee ModalPopup as TargetControlID--%>
            <asp:LinkButton ID="lnkFake" runat="server"></asp:LinkButton>
            <%--pnlAddUpdateEmployeeDetails Panel With Design--%>
            <asp:Panel ID="pnlAddUpdateEmployeeDetails" runat="server" CssClass="modalPopup"
                Style="display: none;">
                <div style="overflow-y: auto; overflow-x: hidden; max-height: 450px;">
                    <div class="modal-header">
                        <asp:Label ID="lblHeading" runat="server" CssClass="modal-title"></asp:Label>
                    </div>
                    <div class="modal-body">
                        <div class="form-group">
                            <div class="row">
                                <div class="col-md-3">
                                    <label for="txtName">
                                        Name</label>
                                </div>
                                <div class="col-md-6">
                                    <asp:TextBox ID="txtName" runat="server" CssClass="form-control" placeholder="Name"
                                        Width="150px"></asp:TextBox>
                                </div>
                                <div class="col-md-3">
                                    <asp:RequiredFieldValidator ID="rfvName" Display="Dynamic" ValidationGroup="Employee"
                                        ErrorMessage="Required" ControlToValidate="txtName" runat="server" ForeColor="Red" />
                                </div>
                            </div>
                        </div>
                        <div class="form-group">
                            <div class="row">
                                <div class="col-md-3">
                                    <label for="txtCountry">
                                        Country</label>
                                </div>
                                <div class="col-md-6">
                                    <asp:TextBox ID="txtCountry" runat="server" CssClass="form-control" placeholder="Country"
                                        Width="150px"></asp:TextBox>
                                </div>
                                <div class="col-md-3">
                                    <asp:RequiredFieldValidator ID="rfvCountry" ErrorMessage="Required" Display="Dynamic"
                                        ValidationGroup="Employee" ControlToValidate="txtCountry" runat="server" ForeColor="Red" />
                                </div>
                            </div>
                        </div>
                        <div class="form-group">
                            <div class="row">
                                <div class="col-md-3">
                                    <label for="txtSalary">
                                        Salary</label>
                                </div>
                                <div class="col-md-6">
                                    <asp:TextBox ID="txtSalary" runat="server" CssClass="form-control" placeholder="Salary"
                                        Width="150px"></asp:TextBox>
                                    <uc:FilteredTextBoxExtender ID="ftSalary" runat="server" TargetControlID="txtSalary"
                                        FilterType="Custom" ValidChars="1234567890.">
                                    </uc:FilteredTextBoxExtender>
                                </div>
                                <div class="col-md-3">
                                    <asp:RequiredFieldValidator ID="rfvSalary" Display="Dynamic" ValidationGroup="Employee"
                                        ErrorMessage="Required" ControlToValidate="txtSalary" runat="server" ForeColor="Red" />
                                </div>
                            </div>
                        </div>
                    </div>
                    <div align="center" class="modal-footer">
                        <div class="row">
                            <div class="col-md-12">
                                <asp:HiddenField ID="hfAddEditEmployeeId" runat="server" Value="0" />
                                <asp:HiddenField ID="hfAddEdit" runat="server" Value="ADD" />
                                <asp:Button ID="btnSave" runat="server" Text="ADD" OnClick="Save" class="btn btn-success"
                                    ValidationGroup="Employee"></asp:Button>
                                <button id="btnCancel" runat="server" class="btn btn-primary">
                                    Cancel
                                </button>
                            </div>
                        </div>
                    </div>
                </div>
            </asp:Panel>
            <%--mpeAddUpdateEmployee Modal Popup Extender For pnlAddUpdateEmployeeDetails--%>
            <uc:ModalPopupExtender ID="mpeAddUpdateEmployee" runat="server" PopupControlID="pnlAddUpdateEmployeeDetails"
                TargetControlID="lnkFake" BehaviorID="mpeAddUpdateEmployee" CancelControlID="btnCancel"
                BackgroundCssClass="modalBackground">
            </uc:ModalPopupExtender>
            <%--lnkFake1 Link Button for mpeDeleteEmployee ModalPopup as TargetControlID--%>
            <asp:LinkButton ID="lnkFake1" runat="server"></asp:LinkButton>
            <%--pnlDeleteEmployee Panel With Design--%>
            <asp:Panel ID="pnlDeleteEmployee" runat="server" CssClass="modalPopup" Style="display: none;">
                <div id="Div1" runat="server" class="header">
                </div>
                <div style="overflow-y: auto; overflow-x: hidden; max-height: 450px;">
                    <div class="form-group modal-body">
                        <div class="row">
                            <div class="col-md-12">
                                Do you Want to delete this record ?
                            </div>
                        </div>
                    </div>
                </div>
                <div align="right" class="modal-footer">
                    <div class="row">
                        <div class="col-md-12">
                            <asp:HiddenField ID="hfDeleteEmployeeId" runat="server" Value="0" />
                            <asp:Button ID="btnYes" runat="server" Text="Yes" OnClick="Yes" class="btn btn-danger">
                            </asp:Button>
                            <button id="btnNo" runat="server" class="btn btn-default">
                                Cancel
                            </button>
                        </div>
                    </div>
                </div>
            </asp:Panel>
            <%-- mpeDeleteEmployee Modal Popup Extender For pnlDeleteEmployee--%>
            <uc:ModalPopupExtender ID="mpeDeleteEmployee" runat="server" PopupControlID="pnlDeleteEmployee"
                TargetControlID="lnkFake1" BehaviorID="mpeDeleteEmployee" CancelControlID="btnNo"
                BackgroundCssClass="modalBackground">
            </uc:ModalPopupExtender>
        </ContentTemplate>
        <Triggers>
            <asp:AsyncPostBackTrigger ControlID="GridView1" />
        </Triggers>
    </asp:UpdatePanel>
    </form>
</body>
</html>
Code
protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        this.BindEmployee();
    }
}
/* Clear controls values and Set default value to controls */
private void ClearControls()
{
    hfAddEdit.Value = "ADD";
    btnSave.Text = "ADD";
    lblHeading.Text = "Add Employee Details";
    hfAddEditEmployeeId.Value = "0";
    hfDeleteEmployeeId.Value = "0";
    txtCountry.Text = string.Empty;
    txtName.Text = string.Empty;
    txtSalary.Text = string.Empty;
}
/* Bind Employee Grid*/
private void BindEmployee()
{
    /* Code For Bind Employee Grid*/
    string query = "SELECT Id, Name, Country, Salary FROM Employee";
    SqlCommand cmd = new SqlCommand(query);
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    SqlConnection con = new SqlConnection(constr);
    SqlDataAdapter sda = new SqlDataAdapter();
    cmd.Connection = con;
    sda.SelectCommand = cmd;
    DataSet ds = new DataSet();
    sda.Fill(ds);
    GridView1.DataSource = ds;
    GridView1.DataBind();
    /* Apply Bootstrap Collapse and Expand Class for Grid cells attribute*/
    BootstrapCollapsExpand();
}
/* Edit Employee Detail*/
protected void Edit(object sender, EventArgs e)
{
    /* Change label text of lblHeading on Edit button Click */
    lblHeading.Text = "Update Employee Details";
    /* Sets CommandArgument value to hidden field hfAddEditEmployeeId */
    hfAddEditEmployeeId.Value = (sender as Button).CommandArgument;
    /* Sets value from Grid cell to textboxes txtName,txtCountry and txtSalary */
    txtName.Text = ((sender as Button).NamingContainer as GridViewRow).Cells[1].Text;
    txtCountry.Text = ((sender as Button).NamingContainer as GridViewRow).Cells[2].Text;
    txtSalary.Text = ((sender as Button).NamingContainer as GridViewRow).Cells[3].Text;
    /* Change text of button as Update*/
    btnSave.Text = "Update";
    /* Apply Bootstrap Collapse and Expand Class for Grid cells attribute */
    BootstrapCollapsExpand();
    /* Show AddUpdateEmployee Modal Popup */
    mpeAddUpdateEmployee.Show();
}
/*Add Employee Detail*/
protected void Add(object sender, EventArgs e)
{
    /* Clear Controls Value */
    ClearControls();
    /* Apply Bootstrap Collapse and Expand Class for Grid cells attribute */
    BootstrapCollapsExpand();
    /* Show mpeAddUpdateEmployee Modal Popup */
    mpeAddUpdateEmployee.Show();
}
/* Save or Update Employee Details*/
protected void Save(object sender, EventArgs e)
{
    /* Code For INSERT OR UPDATE */
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    SqlConnection con = new SqlConnection(constr);
    /* Set employeeId from hfAddEditEmployeeId value for INSERT or UPDATE */
    int employeeId = Convert.ToInt32(hfAddEditEmployeeId.Value);
    string query = string.Empty;
    /* To Check Employee Id For Insert or Update and sets query string variable text*/
    if (employeeId > 0)
    {
        query = "UPDATE Employee SET Name = @Name, Country = @Country, Salary = @Salary WHERE Id = @Id";
    }
    else
    {
        query = "INSERT INTO Employee(Name, Country, Salary) VALUES(@Name, @Country, @Salary)";
    }
    SqlCommand cmd = new SqlCommand(query);
    if (employeeId > 0)
    {
        cmd.Parameters.AddWithValue("@Id", employeeId);
    }
    cmd.Parameters.AddWithValue("@Name", txtName.Text.Trim());
    cmd.Parameters.AddWithValue("@Country", txtCountry.Text.Trim());
    cmd.Parameters.AddWithValue("@Salary", txtSalary.Text);
    cmd.Connection = con;
    con.Open();
    cmd.ExecuteNonQuery();
    con.Close();
    /* Bind Employee Grid*/
    BindEmployee();
    /* Hide mpeAddUpdateEmployee Modal Popup */
    mpeAddUpdateEmployee.Hide();
    /* Clear Controls Value */
    ClearControls();
}
/* Delete Emploee Detail*/
protected void Delete(object sender, EventArgs e)
{
    /* Apply CommandArgument value to hidden field hfDeleteEmployeeId */
    hfDeleteEmployeeId.Value = (sender as Button).CommandArgument;
    /* Apply Bootstrap Collapse and Expand Class for Grid cells attribute*/
    BootstrapCollapsExpand();
    /* Show DeleteEmployee Modal Popup */
    mpeDeleteEmployee.Show();
}
/* If Select Yes on Delete Modal Popup */
protected void Yes(object sender, EventArgs e)
{
    /* Code to Delete Employee Record */
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    SqlConnection con = new SqlConnection(constr);
    int EmployeeId = Convert.ToInt32(hfDeleteEmployeeId.Value);
    SqlCommand cmd = new SqlCommand("DELETE FROM Employee WHERE Id = @Id");
    cmd.Parameters.AddWithValue("@Id", EmployeeId);
    cmd.Connection = con;
    con.Open();
    cmd.ExecuteNonQuery();
    con.Close();
    /* Bind Grid Again To see latest Records*/
    BindEmployee();
    /* Hide Delete Employee Modal Popup */
    mpeDeleteEmployee.Hide();
    /*Clear Controls Value*/
    ClearControls();
}
/* Apply Bootstrap Collapse and Expand Class for Grid cells attribute*/
private void BootstrapCollapsExpand()
{
    if (this.GridView1.Rows.Count > 0)
    {
        //Attribute to show the Plus Minus Button.
        GridView1.HeaderRow.Cells[1].Attributes["data-class"] = "expand";
        //Attribute to hide column in Phone.
        GridView1.HeaderRow.Cells[0].Attributes["data-hide"] = "phone";
        GridView1.HeaderRow.Cells[2].Attributes["data-hide"] = "phone";
        GridView1.HeaderRow.Cells[3].Attributes["data-hide"] = "phone";
        GridView1.HeaderRow.Cells[4].Attributes["data-hide"] = "expand";
        GridView1.HeaderRow.Cells[5].Attributes["data-hide"] = "expand";
        //Adds THEAD and TBODY to GridView.
        GridView1.HeaderRow.TableSection = TableRowSection.TableHeader;
    }
}
Screenshot
WebView

MobileView(Responsive)
