Modified version of the JS trick found here: https://css-tricks.com/findingfixing-unintended-body-overflow/

find-unintended-body-overflow-css.js

var docWidth = document.documentElement.offsetWidth;

[].forEach.call(
  document.querySelectorAll('*'),
  function(el) {
    if (el.offsetWidth > docWidth) {
      el.style.border = "1px solid red";
      console.log(el);
    }
  }
);