Reduce margin between top menu and page title

Hi
I am trying to reduce the margin (space) between the top menu and my page title.
For example when you click my website https://www.joshuaexpert.com
You will notice that between my top menu(the one with home, about and site-map buttons) and the title ‘Site-map’ has some space in between. I am trying to reduce the space but my theme does not provide the option of doing so.
I was wondering if I could edit this in the style.css editor?
If so which line should I look for and what should I change?
Thank you =D