gecko/browser/base/content/highlighter.css

#highlighter-container {
  pointer-events: none;
}

#highlighter-controls {
  position: absolute;
  top: 0;
  left: 0;
}

#highlighter-veil-container {
  overflow: hidden;
}

.highlighter-veil,
#highlighter-veil-middlebox,
#highlighter-veil-transparentbox {
  -moz-transition-property: width, height;
  -moz-transition-duration: 0.1s;
  -moz-transition-timing-function: linear;
}

#highlighter-veil-bottombox,
#highlighter-veil-rightbox {
  -moz-box-flex: 1;
}

#highlighter-veil-middlebox:-moz-locale-dir(rtl) {
  -moz-box-direction: reverse;
}

#highlighter-close-button {
  position: absolute;
  pointer-events: auto;
  z-index: 1;
}