gecko/toolkit/themes/pinstripe/global/tabprompts.css

/* Tab Modal Prompt boxes */
tabmodalprompt {
  background-color: hsla(0,0%,97%,.15);
  background-image: -moz-radial-gradient(center 40%, circle closest-side, hsla(0,0%,90%,.5), hsla(0,0%,90%,0));
}

.mainContainer {
  padding: 20px;
  color: black;
  background-image: -moz-linear-gradient(hsla(0,0%,97%,.9), hsla(0,0%,87%,.9));
  border-radius: 8px;
  box-shadow: 0 0 0 1px hsla(0,0%,0%,.25) inset,
              0 1px 1px hsla(0,0%,0%,.2) inset,
              0 1px 2px hsla(0,0%,0%,.1) inset,
              0 1px 0 hsla(0,0%,100%,.4);
}

.buttonContainer {
  margin-top: 10px;
}

.info\.icon {
  width: 64px !important;
  height: 64px !important;
}

.alert-icon {
  list-style-image: url("chrome://global/skin/icons/information-tabmodal-64.png") !important;
}

.question-icon {
  list-style-image: url("chrome://global/skin/icons/question-tabmodal-64.png") !important;
}