CSS 'missing opening '{' for Parallax

Hi everyone, 

I'm trying this Parallax effect for my personal website. I found this code on an youtube channel : here it's the link. I'm a beginner in Squarespace, so I try again and again ; 0 result with this message 'missing opening '{' .

Can you help me, please? What's wrong?

Thanks a lot in advance ! 

Thanks a lot !!! It works no perfectly but much better. I have to understand more things regarding the blocks of this code injection. 

Have a good day.