How to make a header section like this

Theme: https://avada.theme-fusion.com/music/

I see that the key is position: fixed; But how this exactly work? need a div and?

Thanks

Hey ya, how is going? You can learn everything about HTML/CSS on https://www.w3schools.com/ !

About position:
https://www.w3schools.com/css/css_positioning.asp

EDIT: You have to understand how position works, not only with fixed and etc.