Should flag

This paragraph keeps only 8px between its words and each side of a phone's window, under the 12px a phone gutter needs.

This paragraph keeps 11px between its words and each side of the window, a pixel short of the phone gutter floor.

Should pass

This paragraph keeps a consistent 12px gutter on both sides of a 390px window, the common mobile setting the phone floor allows.

This paragraph keeps 14px on both sides of the window, over the 12px floor that applies at 480px and narrower.

This paragraph keeps a roomy 24px gutter on both sides of the window, well inside the edges of the phone.

Page overflow

• The first item of a list laid out at a fixed desktop width, so every line of it runs past the right edge of the phone and is cut off.
• The second item of the same list, cut off at the same edge, one more line a visitor cannot read the end of on this phone.