This page has the body element (indicated by the red border) without width set. There is a div (blue bordered) with a width of 1200px. The layout viewport width will be set at 1200px (as 1200 > 980) if no viewport meta tag set. With the tag set, on a phone with about 400px viewport width (e.g. Pixel 3), the layout width will be set at the device width about 400px. So the red box and the blue box will exceed the device width.