Their main question was: they have let’s say – they have an HTML page. Some parts of that page are hidden by the CSS Display: none property.
When a user first lands on the page that is hidden, for some reason – perhaps to simplify the user interface.
They wonder if the content that is hidden by the CSS, when a user first lands on a page, can be the target for Google evaluating the site or not?
John explained that this content can still be indexed. So long as the content is in the HTML itself and the DOM (document object model) when the page is loaded, then Google can use that for indexing.
But, so long as it is in the DOM, and if it is in the HTML, then it just goes from being hidden to visible, and this is perfectly fine.
This happens at approximately the 49:16 mark in the video.