Body element (red border; no width set, implicit width of 100%) + div element (blue boder; no width set, implicit width of 100%).

The viewport meta tag is NOT set.

The layout viewport width will be set at 980px by default.

On a phone with about 400px visual viewport width (e.g. Pixel 2), the scale factor of 0.4 (400/980) will be applied. The page looks smaller.

The page body (red) and the div (blue) will occupy the whole screen width.

Compare this with 1-nowidth-meta.html on a mobile device.