Diving into history, creating a mobile version was impossible in the earliest versions of CSS. Viewport units were amended only in 2012 with the introduction of

Diving into history, creating a mobile version was impossible in the earliest versions of CSS. Viewport units were amended only in 2012 with the introduction of CSS3. Prior to that, the only way to create a mobile version was to check the UA and, if it was a mobile device, redirect to a specific HTML page that was adapted for mobile devices. Probably, we will do this in the same way.