message: [Improvement] Slider: expand touch area
diff: background-color: $white;
  transform: translate3d(50%, -50%, 0);
  box-shadow: 0 1px 2px rgba(0, 0, 0, .5);
  +
  + /* use pseudo element to expand touch area */
  + &::after {
  + content: '';
  + position: absolute;
  + width: 200%;
  + height: 200%;
  + top: -50%;
  + left: -50%;
  + }
  }
  &--disabled {
  