Quick script to find elements that are causing horizontal scroll because the overflow the viewport.

overflow.js

function test(which, value) {
  if (value > 0) throw new Error(`${which}: ${value}px`)
}

for (const element of document.querySelectorAll('*')) {
  const { left, right } = element.getBoundingClientRect()
  try {
    test('right', right - window.innerWidth)
    test('left', 0 - left)
  } catch ({ message }) {
    element.style.outline = '2px solid hotpink'
    console.log(`Element outside page bounds (${message})`, element)
  }
}