Without a viewport meta tag, mobile devices render pages at typical desktop screen widths, and then scale the pages to fit the mobile screens. Setting the viewport enables you to control the width and scaling of the viewport. Check out the following links to learn more:
Add a viewport
<meta> tag in the
<head> of your HTML.
<head> ... <meta name="viewport" content="width=device-width, initial-scale=1"> ... </head>
width=device-width key-value pair sets the width of the viewport to
the width of the device. The
initial-scale=1 key-value pair sets the initial
zoom level when visiting the page.
Lighthouse checks that there's a
<meta name="viewport"> tag in the
of the document. It also checks that the node contains a
and that the value of this attribute contains the text
it does not check that
device-width. Lighthouse also does not
check for a
initial-scale key-value pair.