yeah, the 'strong' tag 'can' be manipulated for that div id (button_pm) and avoid the subs.php edit altogether, but.... it's not clean or valid, which means a browser can stop honoring it at any point or a browser may just ignore it as it is right now just to honor it the next time... it can certainly be left in the strong tag, but wrapping it in a class harms nothing yet allows whatever css to be applied that meets the need of the user- square, transparent, float or anchored.... it can even be given an absolute and/or fixed and a z-index above other elements an staying on the screen (upper right, let's say) just so you KNOW it is seen by the user...
i think the point is to just get it into a class where the user can manipulate it at will and with ease, and that is valid.
i'm happy others can take this and use it- it is SO silly a little thing it should have been done a long time ago and addressed by many. at least i should have done it on my own pages a long time ago... it's one of those things that easily fall off the radar, ya know?