Colleagues,
I am new to ASP, though I know a thing or two about C# WinForms (and WebForms in VS 2005... but later VSs have them no more).
I'm using VS 2019, and I go through the Murach's "ASP.NET 4.6 Web Programming with C# 2015" for self-education (I have been told that my next project at work will be Web app for internal use).
I'm now at Ch. 3, where authors show (or try to) how to use CSS on a little project "Future Value Calculator".
This is how it looks:



I dutifully typed the ASPX code from the book (page 81, if you have it) to the project, but when I tried to compile it - I got these error messages:



I, then, just old-faschionedly double-clicked on these buttons on the form in Designer and added codes to both buttons:



... but the errors didn't go away!

What am I'm missing or doing wrong?

Please advise.
(Let me know if you need the actual code snippets.)

Regards,

Ilya