Tribute page columns

I notice when I’m viewing code where people are using bootstrap they can simply use div class=“col-xs-12” and things seem to display correctly

In order for my page to display correctly, I have to use all of the column classes div class=“col-xs-12 col-sm-12 col-md-12 col-lg-12”

Here is a link to my (incomplete) project:

Can someone explain this to me? Thanks!