Remove grey box, blog buttons and blog layout

Hi,

I would like to get rid of this grey box and can't find how. 
picture: https://1drv.ms/u/s!AgnGQQXdd_gk0yA02kax4kDIcMJq
maybe it's not that visible, but there is a grey box under each excerpt

The other question I have is if I can make a blog post in the middle of the page like in this picture:
https://1drv.ms/u/s!AgnGQQXdd_gk0yHaHpctgckyjCm_ 

I see layout options on Theme Options/Blog, but I don't see a layout like that. Is it possible to achieve it somehow please? 

Also, what custom css can I please use to edit the buttons on the blog page. I mean the Read more button. I know the code for styling but I don't know the selector. 

Thanks! 

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