XF 1.4 Add padding to .messageUserBlock + customization (example)

[Betclever]

Dear all,

I found on another template something I want to do on my own template.

In fact, I want to have a space between the avatar block (in a thread) and the messageblock.

This is what I have atm:

This is what I want:

My website is => bet-clever.com
The website where I found this thing is => http://realitygaming.fr/threads/pmu-question-importante-parions-sport.422913/#post-5045075

This option is integrated in this theme and I have it but I don't want to put it by default cause I like the one I have atm but I just want to do something similar at this place.

Thanks for your help.