Several questions about Bootstrap 4.0?

#1

here is my Codepen link:
https://codepen.io/sarah870102/pen/dJXedq?editors=1000

I have several questions:

1.when I use BootStrap 3.0, the image will be set the center of the page, but class=“img-responsive center-block” is invalid when BootStrap 4.0 is adopted.
So how can I set image center when I have to use Bootstrap 4.0?

2.when I use BootStrap 3.0, the image will be set the center of the page, but class =“col-xs-12 col-sm-10 col-sm-offset-1 col-md-8 col-md-offset-2” is also invalid when change to BootStrap 4.0.

So how can I set a list center when I have to use Bootstrap 4.0?

PS:I am totally confused by BootStrap 4.0 when I need to set something center!

Please give me some help, thanks a lot!

#2

.img-responsive moved to .img-fluid
.center-block dropped in favor of .mx-auto

you can also center images by putting
.text-center on the containing block afaik


the documentation is actually really nice

#3