asp.net core mvc password validators

What is the easy way to customize password validation rules in asp.net core MVC? The problem is exactly like someone had here How To Change Password Validation in ASP.Net MVC Identity 2? the only difference is that I’m using asp.net CORE MVC (latest build) with Visual Studio 2015. I’d like to remove all password validation rules. There is no ApplicationUserManager class in the project, also I’m not sure if it’s possible to customize UserManager validation rules in the Startup.cs file.

Change CSS Dynamically

I need to determine which CSS should be applied on some specific pages. I have a master page which has children and default.aspx and services.aspx are ones of the children of Master page. What I want to is when user navigates Default.aspx or Services.aspx,system should apply DefaultCSS file otherwise I want to apply some ordinary css file.