WebConfigurationManager into Class Library

Question

Dear All,

I am trying to use Web.Configuration into Class Library but i m getting below error even though i already added System.Web dll into class library

Error : Cannot apply indexing with [] to an expression of type 'System.Configuration.ConnectionStringSettingsCollection'

using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Data.SqlClient;

using System.Data;

using System.Web.UI;

using System.Web;

using System.Web.Configuration;

namespace DawarLibrary

{

    class MainClass

    {

        public static string _ConString="";

        static MainClass()

        {

            _ConString = WebConfigurationManager.ConnectionStrings["DawarDB_New"].ConnectionString;

        }