Sample eww volume slider demo [Pulse].

eww.scss

* {
  all: unset;
  font-family: "Cooper Hewitt";
}

box {
  padding: 0.5em;
}

scale highlight {
  background-color: darkorchid;
  padding: 0.5em;
  border-radius: 0.2em;
}

scale trough {
  background-color: teal;
  border-radius: 0.2em;
}

// vim:ft=scss

eww.yuck

(defwindow test :geometry
  (geometry :x "20px"
            :y "100px"
            :anchor "center"
            :width "270px"
            :height "60px")
  (scale-test))

(defwidget scale-test []
  (box :orientation "v"
    (scale :onchange "pactl set-sink-volume 0 $(printf %.0f {})%"
           :min 0
           :max 101
           :value "pacmd list-sinks | grep -A 7 '\* index' | grep volume | awk -F/ '{print $2}' | tr -d ' ' | sed 's/%$//'"
           :active true)))

;; vim:ft=yuck

Demo