Bootstrap 4 is a major rewrite of almost the entire project. The most notable changes are summarized immediately below, followed by more specific class and behavioral changes to relevant components
1) Dropped IE8, IE9, and iOS 6 support. v4 is now only IE10+ and iOS 7+. For sites needing either of those, use v3.
2) Added official support for Android v5.0 Lollipop’s Browser and WebView. Earlier versions of the Android Browser and WebView remain only unofficially supported.
1) Flexbox is enabled by default.Read More...