Why are styles not applied immediately when rendering?

Question

css

Greetings.

In Bitrix there is such a feature "transferring all js scripts down". Moves both inline and file scripts down before the closing body
Css remained at the top

Now, after this edit, if you look in Chrome (in Chrome) in incognito mode and press f5, you can see how styles are not applied to some elements immediately. In particular, you can see how the links initially have the default html color (blue), and only after a fraction of a second the style is applied. What is interesting is that if you do not go in incognito mode, then there is no such thing, the styles are displayed immediately.
In Firefox, both in incognito and non-incognito mode, this does not happen either.

It also highlights the drop-down popup window, which, in theory, is activated and becomes visible on click.

Recorded GIF:https://i.imgur.com/KderbrX.gifv
The page itself: alta-profil.ru/client-center/articles/kak-obshit-dom-saydingom/
This happens on all pages of the site.

JS does not control the order in which css files are loaded.