I have a web application which is using a dll of a class library . I am unable to access the app.config value in the class library How to access app.config ...

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I have a web application which is using a dll of a class library . I am unable to access the app.config value in the class library

How to access app.config

ConfigurationSettings.AppSettings["conStr"].ToString();

---> this is returning null value
Also when i try to use ConfigurationManager it says not found or missing assembly reference.

using System.Configuration

is also added .