gecko-dev/browser/themes/shared/aboutSessionRestore.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/. */

.description-wrapper {
  background-image: url("chrome://browser/skin/illustrations/error-session-restore.svg");
  background-repeat: no-repeat;
  background-size: 38%;
  padding-inline-start: 38%;
  background-position: left center;
  min-height: 300px;
}

.description-wrapper:dir(rtl) {
  background-position-x: right;
}

.title {
  background-image: none;
}

#tabsToggle {
  cursor: pointer;
  /* Override button background-color and color from common.css */
  background-color: transparent;
  color: #0a84ff !important;
  -moz-context-properties: fill;
  fill: currentColor;
  border: none;
  padding: 0;
  margin: 0;
  padding-inline-end: 45px;
  position: relative;
}

#tabsToggle:after {
  content: "";
  position: absolute;
  width: 100%;
  height: 100%;
  top: 0;
  inset-inline-start: 0;
  background-image: url("chrome://global/skin/icons/arrow-dropdown-16.svg");
  background-repeat: no-repeat;
  background-size: 20px;
  background-position: right center;
}

#tabsToggle:dir(rtl):after {
  background-position-x: left;
}

#tabsToggle:not(.show-tabs):after {
  transform: scaleY(-1);
}

#tabsToggle.show-tabs > #hideTabs,
#tabsToggle:not(.show-tabs) > #showTabs {
  display: none;
}

.tree-container:not(.expanded) {
  visibility: collapse;
}

.button-container {
  text-align: end;
}

treechildren::-moz-tree-image(icon),
treechildren::-moz-tree-image(noicon) {
  padding-inline-end: 2px;
  margin: 0 2px;
  width: 16px;
  height: 16px;
}

treechildren::-moz-tree-image(noicon) {
  list-style-image: url("chrome://mozapps/skin/places/defaultFavicon.svg");
  -moz-context-properties: fill;
  fill: currentColor;
}
treechildren::-moz-tree-image(container, noicon) {
  list-style-image: url("chrome://browser/skin/window.svg");
}

treechildren::-moz-tree-image(checked) {
  list-style-image: url("chrome://global/skin/icons/check.svg");
  -moz-context-properties: fill, stroke;
  fill: #2292d0;
}
treechildren::-moz-tree-image(checked, selected) {
  fill: white;
  stroke: #0095dd;
}

treechildren::-moz-tree-image(partial) {
  list-style-image: url("chrome://global/skin/icons/check-partial.svg");
  -moz-context-properties: fill, stroke;
  fill: #2292d0;
}
treechildren::-moz-tree-image(partial, selected) {
  fill: white;
  stroke: #0095dd;
}