asp.net - How to disable past dates in a Calendar

How to disable Calendar past previous dates
DisableCalendarPastDates.aspx

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

<!DOCTYPE html>

<script runat="server">
    protected void Calendar1_DayRender(object sender, DayRenderEventArgs e)
    {
        if (e.Day.Date < DateTime.Today)
        {
            e.Cell.Font.Italic = true;
            e.Cell.Font.Size = FontUnit.XLarge;
            e.Day.IsSelectable = false;
            e.Cell.BackColor = System.Drawing.Color.DimGray;
            e.Cell.BorderColor = System.Drawing.Color.Gray;
            e.Cell.ForeColor = System.Drawing.Color.Gray;
            e.Cell.Font.Name = "Courier New";
        }
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>How to disable Calendar past previous dates</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <h2 style="color:SlateBlue; font-style:italic;">
            How to disable Calendar past previous dates
        </h2>
        <hr width="475" align="left" color="SlateGray" />
        <asp:Calendar
            ID="Calendar1" 
            runat="server"
            NextPrevFormat="FullMonth"
            ForeColor="WhiteSmoke"
            SelectionMode="Day"
            DayNameFormat="Full"
            Font-Names="Book Antiqua"
            Font-Size="Medium"
            OnDayRender="Calendar1_DayRender"
            >
            <DayHeaderStyle
                 BackColor="OliveDrab"
                 />
            <DayStyle
                 BackColor="DarkOrchid"
                 BorderColor="IndianRed"
                 BorderWidth="1"
                 Font-Bold="true"
                 Font-Italic="true"
                 Font-Size="Large"
                 />
            <NextPrevStyle
                 Font-Italic="true"
                 Font-Names="Arial CE"
                 />
            <SelectedDayStyle
                 BackColor="Green"
                 BorderColor="SpringGreen"
                 />
            <TitleStyle
                 BackColor="MidnightBlue"
                 Height="36"
                 Font-Size="Large"
                 Font-Names="Courier New Baltic"
                 />
        </asp:Calendar>
    </div>
    </form>
</body>
</html>
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