Every now and then I see a tweet or read an article about z-index. It always bemuses me a little. I rarely find myself trying to figure out the stack of elements with z-index. Perhaps it's the work I do. I don't think that's the case because, being a jobbing freelancer, the work is forever varied.
I've never been a fan of z-index: 9999; the temptation just to make up long numbers to really make sure that the component will be on top is just a little too silly for my liking.
So, for the last 12 months or so I've been using what I call the 'Van Halen method'.
812 1984 5150
Of course, this isn't really any different from 9999, 99999 and 999999 but stipulating the numbers gives me some form of system to make sure I adhere to.
Taking the groups albums titles with numbers in it I've rarely, if ever, found myself needing more than these three options for z-index.
Of course, there's the potential in 6,9,12,24 months that I'll come back to this and laugh at myself. For the moment and for the last year, for me, it's worked perfectly.