Twenty Seventeen theme's Parallax does not work!

Hi Community Support,
I faced a weird problem when I tried to customize my first WP website ,I’m following a tutorial , when the constructor click on customize from the admin dashboard , the theme of twenty seventeen shows up , and it has the parallax effect , but for me it shows up as a static page ,
has anyone faced that before ?
I hope I find an answer, cuz the best thing about the twenty seventeen theme is its parallax effect and I did not get it .

I need help please , anyone faced this problem before ?