Need help with understanding how this animation can be acheived

The animation in the start of the page load, that comes from bottom to top. The whole slides bottom to top but in 6 different frames.

Different ways to build this.
Each of the black bars is set to a 20% width and height that fills the viewport. Possibly fixed to the top with their point of origin set to the top.
Possibly a size interaction where the height changes from 100% (if contained in a 100vh height parent) or 100vh themselves. Changes to 0vh or 0% in height.
The interaction timing is staggered in a way that creates the step effect.