gecko-dev/toolkit/mozapps/extensions/content/blocklist.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/. */

.hardBlockedAddon {
  -moz-binding: url("chrome://mozapps/content/extensions/blocklist.xml#hardblockedaddon");
}

.softBlockedAddon {
  -moz-binding: url("chrome://mozapps/content/extensions/blocklist.xml#softblockedaddon");
}