How to Apply custom css to Billing info form, Order summary section in checkout page

[Kazi-Omar]

We know that for plus store checkout page customization is possible.
as checkout.liquid will deprecate on August 13, 2024 we have to consider checkout UI extension. This extension enables us to include additional components on checkout page.
But how can we apply custom CSS to default forms and sections like (Contact and shipping, Order summary, billing information etc.)?

I know that we can add some custom CSS on the checkout page as a whole but I want to apply CSS more specifically on (Contact and shipping, Order summary, billing information etc.)

How can I achieve that?
I've already checked advanced-checkout-branding and checkout-ui-extension .

[oknaus]

I have the same question. 
If anyone can provide some useful info, it would be much appreciated.