`col-xs-*` not working in Bootstrap 4
问题 I have not encountered this before, and I am having a very hard time trying to find the solution. When having a column equal to medium in bootstrap like so: <h1 class=\"text-center\">Hello, world!</h1> <div class=\"container\"> <div class=\"row\"> <div class=\"col-md-12 text-center\"> <h1>vicki williams</h1> </div> </div> </div> The text-align works fine: But when making the column equal to extra small like so: <div class=\"container\"> <div class=\"row\"> <div class=\"col-xs-12 text-center\"