jquery - How can I export a JavaScript-modified stylesheet? -

i'm working on web app i'm making customisable possible. app has customisation page consists of toolbar , iframe linking dummy preview file. modifications made using toolbar reflected within iframe user able see they're changing. example, there font size input field can used adjust preview page's font-size.

it works this:

<input type="number" id="txtfontsize" value="16" />  $('#sidebar').on('input', '#txtfontsize', function() {     var         previewframe = window.frames['preview'].document,         $body = $('body', previewframe)     ;      $body.css({fontsize:25}) }); 

at bottom of toolbar there save button. i'm needing export javascript-modified stylesheet can store changes particular user. method used saving irrelevant @ point; question this:

how can export default stylesheet along javascript-modified styles?

before asks: format can simple string if easiest. otherwise there under 100 users, wouldn't out of question store these modifications new css files per user instead.