Isotope Rockettheme template top of page issue

The problem is actually the result of your nav bar taking up 2 lines of space when the site template was only designed for the nav bar to occupy 1 line of space... so you will also see this problem occur with other components and not just Event Booking.

That said, you can fix EventBooking by adding the following line of CSS to [Event Booking -> Configuration -> Custom CSS tab -> Custom CSS]: (adjust the 40px value as necessary)

Or is you want to fix the problem for your whole site, consider adding something like this to your site's custom CSS (using whatever means your template provides for modifying template CSS): (again, adjust the 40px to whatever you think looks best)

However, you'll notice that the problem re-appears as screen size decreases and your logo text goes to 3 lines:

And there is too much space when the site drops to mobile menu mode

So... really what you need is some responsive CSS in order to handle all the situations. I will see what I can come up with and post a catch-all solution.