I just tried a different jsfiddle (the previous posted link is now broken) with my desktop browsers.
Vivaldi, Opera Dev, Chrome, Edge = OK
Firefox, Chromium, Ubuntu Web Browser - Windows 10 host, Ubuntu guest VM = OK
Opera (older version) and IE11 = not ok.
My guess is jsfiddle not having a CSS fallback for calc fails.
Safari & iOS Safari (both 6 and 7) does not support viewport units (vw, vh, etc) in calc().