Graphic adjustments to WP6.1 and Twenty Twentythree

Hi, I am trying to create a landing page in WordPress 6.1 and Twenty-Twentythree theme (with Elementor).

I have a couple issues even after visiting “Misha” page.

1) I have set my page template to Empty, still I have a white margin on top of my Elementor contents. Is there a way to get rid of this?

2) Is there a way to add custom CSS to WP 6.1 now that the old section in customize is gone?

3) With the Menu section gone, is there a way to add now a menu in an Elementor block of choice?