No space between photo and title in post grid

Hello, I am using the free version of your plugin and have a problem customizing some elements.
Actually I am using the post grid block on home page (bottom, just above the footer), and there is no space between photo and title.
I can add a margin bottom to the photo in the browser and it works all right, but when I write this change in css/customize, it is not applied at all.
I tried to add a margin-top to the title, same problem..May you help me fix this ?

Would be nice as well to have an option so photos will all be the same size..

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