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 set.

The layout viewport width will be set at device width.

On a phone with about 400px visual viewport width (e.g. Pixel 2), the layout width is also set at about 400px. There is no scaling.

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

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