add style for disabled sliders

[milahu]

i use <input type="slider" disabled> for output values

disabled sliders are read-only, and should have a different style than writable sliders

for example:

/* disable color + cursor */
input[type=range][disabled]::-webkit-slider-thumb {
  background: grey;
  cursor: default;
}
input[type=range][disabled]::-webkit-slider-runnable-track {
  cursor: default;
}

/* disable hover color */
input[type=range][disabled]:hover::-webkit-slider-runnable-track {
  background: white;
}
input[type=range][disabled]:hover::-webkit-slider-thumb {
  background: grey;
}

/* hover color */
input[type=range]:hover::-webkit-slider-runnable-track {
  background: lightgray;
}