@robphat.
Thanks for your advice. I don’t pretend to be a CSS pro (far from it) but I’m already working with Brackets to edit my stylesheets and the developpement tools included in Chrome to click&see where the CSS impacts. I will check that plugin you seem to be so enthusiastic about.
Have a nice day.
@dzung.
Thanks for your reply. I heard a lot about child themes and would like to learn more about it. Do you have a link to a tutorial ? I will try soon your CSS code with the !important and come back to you with the result.
Have a nice day.