roundcubemail/plugins/markasjunk/skins/classic/markasjunk.css

#messagetoolbar a.junk,
#messagetoolbar a.notjunk
{
  text-indent: -5000px;
  background-image: url(images/mail_toolbar.png);
}

#messagetoolbar a.junk
{
  background-position: -32px 0;
}

#messagetoolbar a.junk.pressed
{
  background-position: -32px -32px;
}

#messagetoolbar a.notjunk
{
  background-position: 0 0;
}

#messagetoolbar a.notjunk.pressed
{
  background-position: 0 -32px;
}

ul.toolbarmenu li a.junk,
ul.toolbarmenu li a.notjunk
{
  background-image: url(images/messageactions.png) !important;
  background-repeat: no-repeat;
}

ul.toolbarmenu li a.junk
{
  background-position: 6px -17px !important;
}

ul.toolbarmenu li a.notjunk
{
  background-position: 6px 1px !important;
}