WP Post in rows with different amount of items

Hey there,

I am looking for a solution to display post in rows with different amounts of items. Means first row displays 4 items, second 3, third 4. An example can be found here:

https://codepen.io/joshhowenstine/full/yLqgb/

Is this possible with pure css? CSS Grid Layout? FlexBox?

An additional question:
How can I mix my Post with some customs post? For example, that every third item is a “custom post” instead of post?

Thanks for your help,
I spent some time to find related problems, but coudnt find any answers.