How to create multiple sizes of square box polygon within another polygon using bigquery

I am trying to create sequeries of random polygon of square shapes (the red box) that sits within a larger polygon (the blue polygon), given the larger polygon's geometries. How can I achieve this in big query. I als

I tried the ST_MAKEENVELOP() but it's no found in BQ, as well as ST_XMIN and ST_XMAX