gecko-dev/toolkit/themes/shared/aboutServiceWorkers.css

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

body {
  min-width: 330px;
  max-width: 100%;
  min-height: 330px;
  max-height: 100%;
}

.warningBackground {
  display: none;
  background: -moz-Dialog;
  width:100%;
  height:100%;
  z-index:10;
  top:0;
  left:0;
  position:fixed;
}

.warningMessage {
  color: -moz-FieldText;
  position: relative;
  min-width: 330px;
  max-width: 50em;
  margin: 4em auto;
  border: 1px solid ThreeDShadow;
  border-radius: 10px;
  padding: 3em;
  padding-inline-start: 30px;
  background: -moz-Field;
  margin-left: auto;
  text-align: center;
}

.active {
  display: block;
}

.inactive {
  display: none;
}