css
finding unintended body overflow
with the page on screen, open the browser console, and run this code
var docWidth = document.documentElement.offsetWidth;
[].forEach.call(
document.querySelectorAll('*'),
function(el) {
if (el.offsetWidth > docWidth) {
console.log(el);
}
}
);
look the faulty elements on console
reference: Finding/Fixing Unintended Body Overflow