twentyeleven – less spacing

Hi all,

Sorry if this has been addressed already, but I couldn’t find any post related to this.
I’m trying to decrease the amount of space between the site title / site description and the header image. And also the amount of space between the menu and the page name (“La compagnie” if you have a look at https://soleilsouslapluie.fr/ )

I feel I should mention that I have basic HTML / CSS knowledge, and therefore tried to change quite a few things in the css file already, but so far it’s a complete failure.

Thanks for any help you can provide,
Ilyasou