How to fix DIV in W3.CSS?

[saseda]

In the normal CSS is very easy for me : i make in CSS

div.fixed {
  position: fixed;
  bottom: 150px;
  right: 150px;
  width: 300px;
  border: 3px solid #73AD21;
}

and in HTML

<div class="fixed"></div>

, but in W3.CSS i don't know how to do that...  I want to be responsive and mobile for all devices.

In the lessons of W3.CSS, I found an example only for menu, but not for DIV.