Customizing the external login buttons in Asp.Net Web Forms

Question

I am working on a project that uses the Asp.Net Identity External login to allow users to login to the system using their Google, Facebook, Twitter, Microsoft account. Using the OAuth functionality I have implemented the external login successfully. 

 

The problem is that the external login buttons that appear on the login page are plain white buttons like in the picture below:

 

While I want the buttons to display the image name of the particular provider like in the picture below:

 

 

I have looked into the tutorial provided at this link : (https://www.c-sharpcorner.com/UploadFile/4b0136/working-with-external-providers-in-mvc-5/).

 

How can I implement the same in Asp.Net Web Forms instead of MVC?