Simple Dimmer - ESP8266 - HTTP commands

Looking to add a homemade dimmer setup into OpenHAB.
It is basically a 12V LED strip, ESP8266 and a transistor - using PWM to dim the strip.

Currently a very simple setup where a HTTP command can be passed to the device to select various dimming levels. (http://ipaddress/brightness (0,20,40,50,60,80,100).
Currently have it on OpenHAB as a switchable light (0%/OFF - 100%/ON).
Is it possible to add a dimmer item to OpenHAB using these steps of brightness?
I may be able to change the ESP8266 sketch to accept all levels 0-100 - not just a pre-defined few.
Also not against the idea of putting a premade firmware on it that can handle dimming via a transistor and works better with OpenHAB - I’m yet to look at MQTT solutions.

I can add a line to return current brightness level if needed.

Use the sitemap element Selection
or SetPoint with a set of 20