Hello, Everyone! :-) I am using the "Alpha Pro" theme in HTML Editor. I want to add more "tabs" at the top. When I do, it goes below the 4 existing ones. (see pictures)

How can I do this?

I don't know this particular theme, but the reason why the next button goes on a line below is that it has not got enough space on the same line as the other buttons.

You may try one of these:
Reduce the padding and spacing of the existing buttons
or:
Move the Alpha logo further to the left.

This all will have to be done in the css file.

Or float the logo to the left and increase the size of the box holding the NAV tags, also in the css file.