Know any good tutorial for layout transition animation?

Hi all, I'm looking for a step by step tutorial for transitions like this one (click the girl...) or this one Very simple transitions but still I can't wrap my head around it - even with flexbox - UI elements on the page are constraint. and this is exactly what is appealing in these transitions, they act as if they are unbounded by these constrains and simply fly around from anywhere. Do they switch to absolute and animate with translate() or what... I see this technique everywhere and am looking for a good tutorial to help me solve this riddle...