there is only one single file for both appearances ON and OFF: spr_chk_onoff.svg

you will find the different components identified in the svg such as
<g id="on">
<g id="off">
<g id="disabled_on" opacity="0.3">
<g id="disabled_off" opacity="0.3">

if you have fun inverting the ids you can understand how it works by relying on the svg files previously created for this purpose by alain57 for other forms of the buttons