using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string _RegexAppRoot = @"href=.+?\$appRoot\$";

        var regex = new Regex(_RegexAppRoot);

        string prefix = "https://start-stg.pwc.com/start3/";

        var x = regex.Replace(@"<link rel=""stylesheet"" href=""~/$appRoot$phoenix/styles/bootstrap.min.css"" type=""text/css"" />", "href=\"" + prefix + (prefix.EndsWith("/") ? string.Empty : "/"));

        Console.WriteLine(x);

    }

}