$(document).ready(function() {
  $('#btn_apply').click(function() {
    var uColor        = $('#color').val();
    var uFontFamily   = $('#fontfamily').val();
    var uPadding      = $('#padding').val();
    var uMargin       = $('#margin').val();

    var x = 'background-color: ' + uColor + '; font-family: ' + uFontFamily + '; padding: ' + uPadding + 'px; ' + 'margin: ' + uMargin + 'px; ';
    $('body').attr('style',x);
  });
});