Unable to find Columns and change its style for GridView with AutoGenerateColumns true in ASP.Net

I am trying to add dynamically gridview (headerstylewidth, back-color, height, etc…, itemstyle width, back-color, height, etc…), in codebehind but I am receiving this error:

Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index

See the code:

<asp:GridView
    runat ="server"
    ID="gridview1"
    Height="175px"
    Width="750px"
    GridLines="Both"
    onRowDatabound="gvdata_onRowdataBound">

<Columns >
</Columns >

</asp:GridView>


Private Sub getnum()
 
        Dim fullnum As String = TextBox.Text.Trim()
        Dim HttpClient As HttpResponseMessage = client.GetAsync(Convert.ToString("api/allnumbers? Numbers=") & fullnum).Result
 
        If HttpClient.IsSuccessStatusCode Then
           Dim fnum = HttpClient.Content.ReadAsAsync(Of IEnumerable(Of descriptNumbers))().Result
 
            'Create Table Manually
            Dim dt As New DataTable()
            'Add Columns to DataTable
            dt.Columns.Add("Number", GetType(String))
            dt.Columns.Add("Type", GetType(String))
            dt.Columns.Add("Description", GetType(String))
            dt.Columns.Add("Value", GetType(String))
 
            For Each info In Numbers
                Dim dr As DataRow = dt.NewRow()
                dr("Number") = info.pxNumber
                dr("Type") = info.pxtype
                dr("Description") = info.pxValue
                dr("Value") = info.descType
                dt.Rows.Add(dr)
            Next
 
          Gridview1.DataSource = dt
          Gridview1.DataBind()

ERROR HAPPENS HERE: 
Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index


Gridview1.Columns(0).ItemStyle.Width = Unit.Pixel(75)
Gridview1.Columns(0).HeaderStyle.Width = Unit.Pixel(75)
Gridview1.Columns(0).HeaderStyle.BackColor = Drawing.Color.Gray
Gridview1.Columns(0).HeaderStyle.ForeColor = Drawing.Color.white


Gridview1.Columns(1).ItemStyle.Width = Unit.Pixel(45)
Gridview1.Columns(1).HeaderStyle.Width = Unit.Pixel(45)
Gridview1.Columns(1).HeaderStyle.BackColor = Drawing.Color. Gray
Gridview1.Columns(1).HeaderStyle.ForeColor = Drawing.Color.white

Gridview1.Columns(2).ItemStyle.Width = Unit.Pixel(55)
Gridview1.Columns(2).HeaderStyle.Width = Unit.Pixel(55)
Gridview1.Columns(2).HeaderStyle.BackColor = Drawing.Color. Gray
Gridview1.Columns(2).HeaderStyle.ForeColor = Drawing.Color.white

Gridview1.Columns(3).ItemStyle.Width = Unit.Pixel(225)
Gridview1.Columns(3).HeaderStyle.Width = Unit.Pixel(225)
Gridview1.Columns(3).HeaderStyle.BackColor = Drawing.Color. Gray
Gridview1.Columns(3).HeaderStyle.ForeColor = Drawing.Color.white

End Sub

Protected Sub gvdata_OnRowDataBound(sender As Object, e As System.Web.UI.WebControls.GridViewRowEventArgs)
        If e.Row.RowType = DataControlRowType.DataRow Then
           
           e.Row.Cells(0).BackColor = Drawing.Color.LightBlue
            e.Row.Cells(0).Font.Size = 10
            e.Row.Cells(0).ForeColor = Drawing.Color.Red
            e.Row.Cells(0).HorizontalAlign = HorizontalAlign.Right
           
        End If
    End Sub