Why are columns disappearing in bootstrap?

Question

HTML

Both columns take up 100% of the screen width. I want to swap the columns, but for some reason they completely disappear. What is the reason? push push seems to be correct

<div class="row">
    <div class="col-lg-12 col-lg-push-12">2</div>
    <div class="col-lg-12 col-lg-pull-12">1</div>
  </div>

Answer 1

I'm trying to understand what you want to change? What's the logic? Are you familiar with Bootstrap?
push and pull change block positions in a similar way:

<div class="container">
  <div class="row">
    <div class="col-lg-6 col-lg-push-6">2</div>
    <div class="col-lg-6 col-lg-pull-6">1</div>
  </div>
</div>

why swap something that goes under each other ??? if you can initially change it with handles in the code