<style>
    .k-grouping-dropclue {
        z-index: 10002 !important;
    }
</style>

<TelerikWindow Modal="true"
               @bind-Visible="@isModalVisible"
               CloseOnOverlayClick="true">
    <WindowTitle>
        Window Title
    </WindowTitle>
    <WindowContent>
        <TelerikGrid Data="@GridData"
                     Pageable="true"
                     Sortable="true"
                     Reorderable="true"
                     Height="400px">
            <GridColumns>
                <GridColumn Field="Name" Title="Product Name" />
                <GridColumn Field="Price" DisplayFormat="{0:C2}" />
                <GridColumn Field="@nameof(Product.Released)" DisplayFormat="{0:D}" />
                <GridColumn Field="@nameof(Product.Discontinued)" />
            </GridColumns>
        </TelerikGrid>
    </WindowContent>
    <WindowActions>
        <WindowAction Name="Close" />
    </WindowActions>
</TelerikWindow>

<TelerikButton OnClick="@( _ => isModalVisible = true )">Open the window</TelerikButton>

@code {
    private bool isModalVisible { get; set; } = true;
    private List<Product> GridData { get; set; }

    protected override void OnInitialized()
    {
        GridData = new List<Product>();

        var rnd = new Random();

        for (int i = 1; i <= 30; i++)
        {
            GridData.Add(new Product
                {
                    Id = i,
                    Name = "Product name " + i,
                    Price = (decimal)(rnd.Next(1, 50) * 3.14),
                    Released = DateTime.Now.AddDays(-rnd.Next(1, 365)).AddYears(-rnd.Next(1, 10)).Date,
                    Discontinued = i % 5 == 0
                });

        }

        base.OnInitialized();
    }

    public class Product
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public decimal Price { get; set; }
        public DateTime Released { get; set; }
        public bool Discontinued { get; set; }
    }
}