Paste this in your browser console to search for HTML elements which extend past the window's width and create a horizontal scrollbar.

find-elem-with-breakout-width.js

function findBreakoutElem(rootElem = document.body) {
  function checkElemWidth(elem) {
    if (elem.clientWidth > window.outerWidth) {
      console.log("The following element has a larger width than the window's outer width");
      console.log(elem);
      console.log('<-------------------------------------------------------------------->');
    } else if (elem.scrollWidth > window.outerWidth) {
      console.log("The following element has a larger width than the window's scroll width");
      console.log(elem);
      console.log('<-------------------------------------------------------------------->');
    }

    // Recursively check all the children
    // of the element to find the culprit.
    [...elem.children].forEach(checkElemWidth);
  }
  
  checkElemWidth(rootElem);
}