Two buttons causing one action, why doesn't one of them work?

Question

css

Hello.
The page has one modal window. His call hangs on two buttons, that is, when you click either on the first or on the second, this window should open. For reasons I do not understand, a window opens only by clicking on the button at the top of the page.

Answer 1

Because you don't know how ID stands for

Answer 2

Instead of id(#)button use class(.)button to make 2-3-4-5-...-100500 buttons work.

Answer 3

id must be unique. two elements with the same id is a blunder.