.tabbrowser-tab[first-visible-tab="true"] .tab-background::before,
.tab-background::after {
  content: "";
}

.tab-background::before,
.tab-background::after {
  /* Box Model */
  display: block;
  position: absolute;

  /* Position */
  top: 50%;
  transform:  translateY(calc(-50% + 1px)) !important;

  /* Bar shape */
  width: 0px;
  height: 100%;

  /* Bar Color */
  opacity: 0.3;
  border-right: 1px solid var(--lwt-background-tab-separator-color, currentColor) !important;
}
.tab-background::after {
  right: 0;
}

.tabbrowser-tab[visuallyselected] .tab-background::before,
.tabbrowser-tab[visuallyselected] .tab-background::after,
.tabbrowser-tab[beforeselected-visible] .tab-background::after {
  @include Option("userChrome.tab.static_separator.selected_accent") {
    --lwt-background-tab-separator-color: var(--tab-line-color, var(--lwt-tab-line-color, rgb(10, 132, 255)));
  }
  @include NotOption("userChrome.tab.static_separator.selected_accent") {
    opacity: 0;
  }
}

/* Animate */
@include Animate {
  .tab-background::before,
  .tab-background::after {
    transition: opacity 0.2s var(--animation-easing-function); /* cubic-bezier(.07, .95, 0, 1) */
  }
}