Featured image alignment center

Hi,
I’d like to get featured image aligned center in post list, specifically, standard post list: Hueman

Right now, there is one post which is featured on top of the site and the others are shown below with smaller thumbnail.
The small featured images are not centered but located at the top of each boxes.
I want to make them centered whether the size of images are streched or not.
Can somebody exlplain me how to fix it?

The page I need help with: [log in to see the link]