how to make this "div" always visible to users

Answer 1

You want the {position:fixed} style as well. That will make the top and left be relative to the browser viewport.

Answer 2

Use this

  div.notifier {
       padding:10px;
       height:auto;
       width:auto;
       background-color:white;
       border:1px solid black
       position:fixed;
       top: /*Put the value you want here*/ ;
       left: /*Put the value you want here, if you want to put the div on the right you should use right instead of left*/ ;
   }