Centers the new slider on Feedly

FeedlyCenteredSlider.user.js

// ==UserScript==
// @name       Feedly Centered Slider
// @namespace  http://salvatorelab.es
// @version    2.0
// @description  Centers the slider on Feedly
// @match      http://feedly.com/*
// @grant GM_addStyle
// @require    http://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js
// ==/UserScript==

function centerContentAndArrows() {
  var floatingContent = document.getElementsByClassName('floatingEntryContent')[0];
  if (floatingContent !== undefined) {
    var contentWidth = floatingContent.offsetWidth;
    floatingContent.style = "right: calc(50% - " + (contentWidth/2) + "px) !important;";
  
    var side = ($( window ).width() - contentWidth)/2 + 25;
    GM_addStyle(".slideBumper-right {right: "+side+"px;}");
    GM_addStyle(".slideBumper-left {left: "+side+"px;}");
  }
}

function centerHeader() {
  var floatingContent = document.getElementsByClassName('floatingEntryContent')[0];
  if (floatingContent !== undefined) {
    var contentWidth = floatingContent.offsetWidth;
    floatingContent.style = "right: calc(50% - " + (contentWidth/2) + "px) !important;";
    var header = $('.floatingEntryContentSlide .shareBarFixedHolder .headerInfo');
    header.css('right', '50%').css('right', '-=' + (contentWidth/2) + 'px');
  }
}


//arrows
GM_addStyle(".bumperHolder {position: relative !important;");
GM_addStyle(".slideBumper-right {position: fixed !important; right: 0px; left: auto !important;}");
GM_addStyle(".slideBumper-left {position: fixed !important; left: 0px; right: auto !important;}");

window.onresize = function() {
  centerContentAndArrows();
  centerHeader();
};


var insertedNodes = [];
var observer = new MutationObserver(function(mutations) {
    mutations.forEach(function(mutation) {
      for(var i = 0; i < mutation.addedNodes.length; i++) {
        if (mutation.addedNodes[i].classList.contains('floatingEntryContent')) {
          centerContentAndArrows();
        }
        if (mutation.target.classList.contains('headerInfo')) {
          centerHeader();
        }
      }
    });
});
observer.observe(document, {
  childList: true,
  subtree: true
});