How can I customize a SharePoint Page with no left-side navigation and Search on top?

Question

I need to create the layout bellow in SharePoint Online.

Please notice this requirements:

1. There should be no left side navigation.
2. The Search functionality should be on the top right corner.
3. The page should be responsive so that, in small screens, web parts that are side-by-side should get on top of each other instead.

Answer 1

1. There should be no left left side navigation. = You can change it by, clicking on gear, change the look then at the bottom you see the classic change the look option, click it, you will be redirected to the classic page on changing the looks option, click the current layout, then at the left side, you can see a dropdown option for site layout, change the 'Seatle' to 'Oslo' then save it, see the update in the site.

   2. The Search functionality should be on the top right corner. = Im not sure if this is doable in modern, you can create a custom webpart dedicated for this piece via spfx webpart but it would be a bit overkill

   3. The page should be responsive so that, in small screens, web parts that are side-by-side should get on top of each other instead. = Modern sharepoint will do this for you. You can also test it out in their SharePoint App, its in the apps store.

Let me know if the concept helps, happy learning!