Why after click I can't see how ".firstBlock" coming back?

Question

I put the code responsible for this operation in the comments /* Start */ and /* End */ in JS.
https://code.sololearn.com/WaHGl5IV7U8T/?ref=app

Answer 1

Is it a quiz show question,
or I didnt catch you?
The function should be look as follows:

function turnback() {
$(".firstBlock").toggleClass("altFirstBlock");
}