Changing sidebar font size

Hello,

I’m looking to decrease the size of the font in my sidebars, both on my normal pages and on the posts.
I found a lot of topics with a lot of different codes. I tried them all in the file that opens straight away when you edit the CSS in the appearance tab. But none work.

I’m not sure if I place them wrong, that it has to do with the fact it’s a manually set sidebar, or if I use the wrong codes, but I simply don’t manage.

Hoping someone can help me out.
Thank you!

The page I need help with: [log in to see the link]