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

:scope {
  --border-color: #e5e5e5;
}

#narrate-toggle > svg {
  display: block;
  margin: 0 8px;
}

.dropdown-popup button {
  background-color: transparent;
}

.dropdown-popup button:hover:not(:disabled) {
  background-color: #eaeaea;
}

.narrate-row {
  display: flex;
  align-items: center;
  min-height: 40px;
  box-sizing: border-box;
}

.narrate-row:not(:first-child) {
  border-top: 1px solid var(--border-color);
}

/* Control buttons */

#narrate-control > button {
  background-size: 24px 24px;
  background-repeat: no-repeat;
  background-position: center center;
  height: 64px;
  width: 100px;
  border: none;
  color: #666;
  box-sizing: border-box;
}

#narrate-control > button:not(:first-child) {
  border-left: 1px solid var(--border-color);
}

#narrate-skip-previous {
  border-top-left-radius: 3px;
  background-image: url("chrome://global/skin/narrate/back.svg#enabled");
}

#narrate-skip-next {
  border-top-right-radius: 3px;
  background-image: url("chrome://global/skin/narrate/forward.svg#enabled");
}

#narrate-skip-previous:disabled {
  background-image: url("chrome://global/skin/narrate/back.svg#disabled");
}

#narrate-skip-next:disabled {
  background-image: url("chrome://global/skin/narrate/forward.svg#disabled");
}

#narrate-start-stop {
  background-image: url("chrome://global/skin/narrate/start.svg");
}

#narrate-dropdown.speaking #narrate-start-stop {
  background-image: url("chrome://global/skin/narrate/stop.svg");
}

/* Rate control */

#narrate-rate::before, #narrate-rate::after {
  content: '';
  width: 48px;
  height: 40px;
  background-position: center;
  background-repeat: no-repeat;
  background-size: 24px auto;
}

#narrate-rate::before {
  background-image: url("chrome://global/skin/narrate/slow.svg");
}

#narrate-rate::after {
  background-image: url("chrome://global/skin/narrate/fast.svg");
}

#narrate-rate-input {
  margin: 0 1px;
  flex-grow: 1;
}

#narrate-rate-input::-moz-range-track {
  background-color: #979797;
  height: 2px;
}

#narrate-rate-input::-moz-range-progress {
  background-color: #2EA3FF;
  height: 2px;
}

#narrate-rate-input::-moz-range-thumb {
  background-color: #808080;
  height: 16px;
  width: 16px;
  border-radius: 8px;
  border-width: 0;
}

#narrate-rate-input:active::-moz-range-thumb {
  background-color: #2EA3FF;
}

/* Voice selection */

.voiceselect {
  width: 100%;
}

.voiceselect > button.select-toggle,
.voiceselect > .options > button.option {
  -moz-appearance: none;
  border: none;
  width: 100%;
  min-height: 40px;
}

.voiceselect.open > button.select-toggle {
  border-bottom: 1px solid var(--border-color);
}

.voiceselect > button.select-toggle::after {
  content: '';
  background-image: url("chrome://global/skin/narrate/arrow.svg");
  background-position: center;
  background-repeat: no-repeat;
  background-size: 12px 12px;
  display: inline-block;
  width: 1.5em;
  height: 1em;
  vertical-align: middle;
}

.voiceselect > .options > button.option:not(:first-child) {
  border-top: 1px solid var(--border-color);
}

.voiceselect > .options > button.option  {
  box-sizing: border-box;
}

.voiceselect > .options:not(.hovering) > button.option:focus {
  background-color: #eaeaea;
}

.voiceselect > .options:not(.hovering) > button.option:hover:not(:focus) {
  background-color: transparent;
}

.voiceselect > .options > button.option::-moz-focus-inner {
  outline: none;
  border: 0;
}

.voiceselect > .options {
  display: none;
  overflow-y: auto;
}

.voiceselect.open > .options {
  display: block;
}

.current-voice {
  color: #7f7f7f;
}

.voiceselect:not(.open) > button,
.option:last-child {
  border-radius: 0 0 3px 3px;
}