How to customize/configure cutom Login UI for Identity Server 4 based on their Quickstart Repo

I don't have good knowledge of Identity server in ASP.NET Core, but I found this link http://www.identityserver.com/documentation/admin-ui/configuration-integration/configuring-adminui/

Which says you can define

• UiUrl: Url of the AdminUI frontend (the idxui container)

You can find it in

env.js

• AuthorityUrl: Url of the IdentityServer installation protecting AdminUI
• ApiUrl: Url of the AdminUI backend (the idxapi container)
• UiUrl: Url of the AdminUI frontend (the idxui container)
• AddUserPassword: Allows for settings user passwords on creation. This is for demo purposes only. Do not use in Production.

Another one which may help 

https://leastprivilege.com/2017/10/28/templates-for-identityserver4-v2/

Similar question asked here https://stackoverflow.com/questions/35795394/identityserver3-custom-login-and-registration-screen

Says, "Yes, it is possible, see the documentation on customizing views"

The views in IdentityServer can be customized in one of two ways: 1) Customize the HTML templates provided by the DefaultViewService, or if more control is needed 2) define a custom IViewService.

Another link which explained Angular 2 Open Id integration https://damienbod.com/2016/03/02/angular2-openid-connect-implicit-flow-with-identityserver4/

http://estynedwards.com/blog/2016/01/30/ServiceStack-IdentityServer-Angular/

Hope it helps