`col-xs-*` not working in Bootstrap 4

They dropped XS because Bootstrap is considered a mobile-first development tool. It's default is considered xs and so doesn't need to be defined.

col-xs-* have been dropped in Bootstrap 4 in favor of col-*.

Replace col-xs-12 with col-12 and it will work as expected.

Also note col-xs-offset-{n} were replaced by offset-{n} in v4.

I just wondered, why col-xs-6 did not work for me but then I found the answer in the Bootstrap 4 documentation. The class prefix for extra small devices is now col- while in the previous versions it was col-xs.

https://getbootstrap.com/docs/4.1/layout/grid/#grid-options

Bootstrap 4 dropped all col-xs-* classes, so use col-* instead. For example col-xs-6 replaced by col-6.