Thanks for posting queries in PSC.
I hope you got this css from below article
If you go through this above example you see the HTML file with the container structure of the checkbox as a slider. In css with respective to elements they applied the styles.
In the same we have to customise the checkbox control and apply the css.
To apply the css for checkbox control follow below steps:
1) Get the Id/class of the checkbox and the parent element by inspecting it using developer tools.
2) replace with class/id of that parent element and the checkbox in the above css you shared and place it in the userworkform
I hope this information helps you