asp.net - How to add CheckBox in Calendar day cell

How to add CheckBox control in Calendar Day Cell
AddCheckBoxControlInCalendarDayCell.aspx

<%@ Page Language="C#" AutoEventWireup="true" %>

<!DOCTYPE html>

<script runat="server">
    protected void Calendar1_DayRender(object sender, DayRenderEventArgs e)
    {
        if (e.Day.IsSelected)
        {
            CheckBox CheckBox1 = new CheckBox();
            CheckBox1.Checked = true;
            CheckBox1.Width = 25;
            CheckBox1.Enabled = false;
            e.Cell.Controls.AddAt(1, CheckBox1);
            e.Cell.Font.Size = FontUnit.XLarge;
        }
    }

    protected void Page_Load(object sender, System.EventArgs e)
    {
        if (Page.IsPostBack && Calendar1.SelectedDates.Count ==1)
        {
            Calendar1.SelectedDates.Clear();
        }
    }
    
    protected void Calendar1_SelectionChanged(object sender, System.EventArgs e)
    {
        ListItem li = new ListItem();
        li.Text = Calendar1.SelectedDate.ToShortDateString();

        int itemCounter = 0;
        foreach (ListItem litem in BulletedList1.Items)
        {
            if (litem.Text == li.Text)
            {
                itemCounter += 1;
            }
        }

        if (itemCounter > 0)
        {
            BulletedList1.Items.Remove(li);
        }
        else
        {
            BulletedList1.Items.Add(li);
        }
                
        Calendar1.SelectedDates.Clear();
        SelectedDatesCollection dates = Calendar1.SelectedDates;
        
        foreach (ListItem litem in BulletedList1.Items)
        {
            DateTime date = Convert.ToDateTime(litem.Text);
            dates.Add(date);
        }
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>How to add CheckBox control in Calendar Day Cell</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <h2 style="color:SlateBlue; font-style:italic;">
            How to add CheckBox control in Calendar Day Cell
        </h2>
        <hr width="600" align="left" color="SlateGray" />
        <asp:BulletedList
             ID="BulletedList1"
             runat="server"
             Visible="false"
             >
        </asp:BulletedList>
        <asp:Calendar
            ID="Calendar1" 
            runat="server"
            NextPrevFormat="FullMonth"
            ForeColor="WhiteSmoke"
            SelectionMode="Day"
            DayNameFormat="Full"
            Font-Names="Book Antiqua"
            Font-Size="Medium"
            OnSelectionChanged="Calendar1_SelectionChanged"
            OnDayRender="Calendar1_DayRender"
            >
            <DayHeaderStyle
                 BackColor="OliveDrab"
                 />
            <DayStyle
                 BackColor="DarkOrange"
                 BorderColor="Orange"
                 BorderWidth="1"
                 Font-Bold="true"
                 Font-Italic="true"
                 Font-Size="Large"
                 />
            <NextPrevStyle
                 Font-Italic="true"
                 Font-Names="Arial CE"
                 />
            <SelectedDayStyle
                 BackColor="DarkOrange"
                 BorderColor="Pink"
                 />
            <TitleStyle
                 BackColor="MidnightBlue"
                 Height="36"
                 Font-Size="Large"
                 Font-Names="Courier New Baltic"
                 />
        </asp:Calendar>
    </div>
    </form>
</body>
</html>
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