How to make that Green box to appear on clicking that Red box

Question

I want to get it by Id assign it to a variable then use to make the third green appear
https://code.sololearn.com/W6LGd6lSvZmu/?ref=app

Answer 1

When you select button, you use "document.getElementsByTagName" so you choose all elements with tag button, and you got array. (when your selector have elementS, it will always return array)
So you need to access your button with index

https://code.sololearn.com/WRxEZhjcKue7/?ref=app