i want add calendar on textbox with time.

Backend. for C# 

    protected void btnSave_Click(object sender, EventArgs e)
    {
       
        string selectedDateTime = hiddenField.Value;

      
        string connectionString = "YourConnectionString";
        using (SqlConnection connection = new SqlConnection(connectionString))
        {
            connection.Open();

            string insertQuery = "INSERT INTO YourTable (YourDateTimeColumn) VALUES (@SelectedDateTime)";
            using (SqlCommand command = new SqlCommand(insertQuery, connection))
            {
                command.Parameters.AddWithValue("@SelectedDateTime", DateTime.Parse(selectedDateTime));
                command.ExecuteNonQuery();
            }
        }
    }