When using viewport units, specifically 100vw in this scenario, it will not take into consideration any zoom level. For example, I have a <div> that I want to span the entire width of the page, so I give it a style of width=100vw. If I zoom out (View -> Zoom Out) it no longer takes up the entire width. I have a Stack Overflow issue created here: http://stackoverflow.com/questions/41817411/safari-100vw-layout-issue-when-zoomed-help-me-understand And a jsFiddle here: https://jsfiddle.net/4vax8Lga/ I would expect that 100vw should take up the entire width of the screen, even when zoomed out.