It is an announcement from the FleetKraft team, for example a new feature, planned maintenance or a change to prices. Office staff see it at the top of every page of the web app; drivers, customer portal and subcontractor logins do not. If it has a link, press it to open the page it is about.
Press the cross to close it. It stays closed for you; your colleagues see it until they close it themselves. Some announcements are also emailed once to your company's Admins.