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i3 wm sound volume and brightness

Two questions:
- How to bind hot key so that there would have volume sound display on screen?
- How to bind hot key so that brightness would also display on screen? 

My i3 config for sound volume and brightness is https://paste.debian.net/1009555

The problem is configuration for sound works but there is no display. And for brightness, xbacklight -inc N or xbacklight -dec N returns message 

    No outputs have backlight property

I read that's because xbacklight can't find the corresponded backlight in /sys/class. I am aware that changing the value at /sys/class/backlight/intel_backlight works, but I am looking for somewhat more portable way. 
i3-wm 4.13-1
debian 9.3