How to display javascript banner in website header?

It’s there and visible in Incognito mode, it’s being blocked by one of the adBlocker extension that you might be using in your browser.

The best workaround would be is to change the class from headad to something more generic like head-banner.

Make sure you update the style in your theme/plugin.

Blocked by adblock

Banner with updated class:

Banner with updated class and style