How to create an on/off switch with Javascript/CSS?

check out this generator: On/Off FlipSwitch

you can get various different style outcomes and its css only - no javascript!

You mean something like IPhone checkboxes? Try Thomas Reynolds' iOS Checkboxes script:

Once the files are available to your site, activating the script is very easy:

...

$(document).ready(function() {
  $(':checkbox').iphoneStyle();
});

Results: