Customizable icon size

Not without scaling images, which is something I try to avoid.

You can always use CSS to scale them.

is it something simple?
What should I add in the css? for example to have 40px x 40px?

What I would do is select the 64×64 icons and add the following to your style.css:

.socialmedia-buttons img {
      width: 40px;
      height: 40px;
}

Always better to scale down than to scale up.

Excellent!! It works, thank you.
Resolved

My pleasure.