ASP.NET Identity login with custom Facebook & Google buttons

I creating a website that uses Facebook & Google authentication for account registration. I have it functioning correctly, but I want to customize the buttons that display on the Login page. I'm not sure how these buttons are being created. On the Login.cshtml page:

<section id="socialLoginForm">
    @Html.Partial("_ExternalLoginsListPartial", new ExternalLoginListViewModel { ReturnUrl = ViewBag.ReturnUrl })
</section>

From the rendered HTML page:

<form action="/Account/ExternalLogin" method="post"><input name="__RequestVerificationToken" type="hidden" value="BHNMCUkwp2vT26dQmD98yK52RaMQ18VkBeuH8ukS15WbRxofMAdbrGOoc0qS6HWvRUWgnJM6_tlkaDktGwCQVKS6hiD_gsH8242nckCrzBE6HKgH-OZsETVWj5nYYcxWj8u7nQ8CpFK6KzR8rDJyrg2" />            
    <div id="socialLoginList">
        <p>
            <button type="submit" class="btn btn-default" id="Google" name="provider" value="Google" title="Log in using your Google account">Google</button>
            <button type="submit" class="btn btn-default" id="Facebook" name="provider" value="Facebook" title="Log in using your Facebook account">Facebook</button>
        </p>
    </div>
</form>

I'm not sure how I can create a different stylized custom button for Facebook and Google and have them link directly to the appropriate external login pages?