You are probably missing the viewport meta tag in the html head:
<meta name="viewport" content="width=device-width, initial-scale=1">
Without it the device assumes and sets the viewport to full size.
More info here.
You are probably missing the viewport meta tag in the html head:
<meta name="viewport" content="width=device-width, initial-scale=1">
Without it the device assumes and sets the viewport to full size.
More info here.