Fixed Header

I am trying to find information on how to keep the header and menu permanently fixed at the top of the page with the rest of the site scrolling underneath it.

in this case… The cat logo would remain where it is as would the menu
https://www.vootraslado.com.br

is their a plugin for this, of is this requiring a level of CSS that I simply do not possess?

If this theme had a sticky header option, it would be brilliant.

thank you