Where can I find the featured image in Theme Editor?

Hopefully this doesn’t count as a double-post, but a little update.

I used inspect element to find that my featured image was div class=post_image.
I found post_image in the css style sheet, and added the following:

display: block;
    margin-left: auto;
    margin-right: auto

Yet the image remains uncentered?

Hi workharder! providing the website url will be very helpful.

Hi workharder! providing the website url will be very helpful.

Ah of course – https://nzt-services.com/landing-page/

I dont see any post or page that uses a featured image, do you have one?