typo in style-rtl.css

html.js fieldset.collapsible legend a {
  padding: 0 0 0 15px;
  background: url("images/arrow-down-white.gif") no-repeat left 4px;
}
html.js fieldset.collapsed legend a {
  background: url(images/arrow-left-white.gif) no-repeat left 4px;
}

"gif" should be changed to "png"