Two CSS classes on one div not working

I have this css from bootstrap.min:

.rew {
  margin-right: auto;
  margin-left: auto;
  margin-top: 20px;
  width: 1050px;
}

.rew2 {
  margin-right: auto;
  margin-left: auto;
  margin-top: 20px;
  width: auto;
}

And my div like this (I've red examples from question and answer in stackoverflow):

<div class="rew rew2">
content.....
</div>

The (rew2) it's for responsived css, but before that I was wrote the css on my responsive css file, but it's not working the "div tag" always calls css from bootstrap.min css file. So I wrote two classes in the bootstrap.min css file, but not working also. The "div" tag only called the "rew" class and the "rew2" was ignored.

******** The class on responsive css file was deleted and I wrote the class on bootstrapmin css file

The differences it's only on width, if the site opened from desktop it would have 1050px width, and for the responsive (opened from smartphone) it will automatically adjust the template with the smartphone screen as "auto".

*Huft...I'm so confused why it's not working. I need help from you guys.

Thank you,

Best regards,

Kris