Web folder content moved up a level - Craft Path settings
To replicate what you did in craft 2, you would change your web/index.php to:

define('CRAFT_BASE_PATH', dirname(__DIR__,1) . '/nameofthefolderwherecraftlives');


The ,1 tells craft to go up 1 level and change /nameofthefolderwherecraftlives to well... The name of the folder where craft lives :)

So for what I show you above, your structure will be:


web


index.php

nameofthefolderwherecraftlives


config
modules
storage
templates
vendor



It's here in the docs.

Hope that helps!