it is not quite that simple. first, that line of text is different depending on whether the viewer is logged in or not.
also, if you make this change in the template file then you have to remember to do it again every time you update phpbb.
or, you have to create a custom style just for this one little change.
I would suggest that you don't bother, nobody but you will care about this or even know that you made this change.
I am available for custom work on a donation basis. Please send me a PM with your needs.
Premium phpBB 3.2 Styles
OK, so what's the speed of dark?