How to disable resize in TinyMCE

hi

I used tinymce in my page...

I want users don't allow to resize it so I used below css:

  .elm
        { direction:rtl;
          resize:none;
          text-align:right;
           height:180px;
            font:bold 18px tahoma;
            }

but it doesn't work..

is there other code for this?

Best Rgards

Neda