How can a Back-end developer enter the Front-end?

Question

Frontend

Hello!
Given: C# (Xamarin, Unity, WinForms), Web (Http, REST, Json)
Purpose: to learn how to create UI and assemble everything into a web application.
TL;DR
I thought I'd figure it out myself. I looked at the vacancies - there are two types of them (React / Angular and ASP.NET Core / MVC).
ASP.NET is closer to me, but the manuals tell how to make a back-end, and I'm interested in learning how to put buttons on the screen.
Google C# UI - offer libraries for ASP.NET (etc. Kendo UI)
So what to read to learn how to make graphical interfaces?
UPD.
Thanks javedimka for the reply!
How can a Back-end developer enter the Front-end?

Answer 1

If you need to learn how to create UI for web applications, then you have no choice but to master the HTML, CSS, JS stack.