How can I customize UI checkout page after upgraded checkout extensibility?

[goldenphoenix]

Hi everyone!
I upgraded to checkout extensibility. Now I want to edit the look of the checkout page (add a few HTML elements, edit HTML and CSS, add javascript). Is there any way I can do this?
I hope to receive everyone's help

[Small_Task_Help]

Hi,

Are you using Shopify Plus?

[goldenphoenix]

Yes, I am using Shopify Plus

[adamcharvat]

seems like you can't 

Shopify is making it impossible to manipulate with the Checkout HTML / DOM (unless you want to use checkout.liquid which will be deprecated)