I am starting to use Overleaf to do my master thesis.

Could I ask how can I implement this modification for all my pages?:

And how can I add this nice colourful box at the beginning of each chapter ? I manage to add the Lenny package and insert the square but I am not sure how to do this box format identically:

I saw this in a thesis that is not mine but I liked a lot the format hehe

Thank a lot for your time and help.