Crowdfunding_Page_Product with CSS and Javascript

have an issue when trying to implement transition between the three showcase page, for a smooth appearing or disappearing of these pages when gaming with display property

i have tried javascript syntax as well as css for transition property but it didn't work. Then i clear these ones. i used pseudo selectors to style the shadowing effect of the main page when appearing either the modal-default-page or the thankfullness-page

missing key how can i setttle this matter to make the design perform with transition property

Thanks dude!