metamask-extension/ui/app/css/itcss/components/tab-bar.scss

.tab-bar {
  display: flex;
  flex-direction: column;
  justify-content: flex-start;
}

.tab-bar__tab {
  display: flex;
  flex-flow: row nowrap;
  align-items: flex-start;
  min-width: 0;
  flex: 0 0 auto;
  box-sizing: border-box;
  font-size: 16px;
  padding: 16px 24px;
  opacity: .5;
  transition: opacity 200ms ease-in-out;

  @media screen and (min-width: 576px) {
    &:hover {
      opacity: .4;
    }

    &:active {
      opacity: .6;
    }
  }

  @media screen and (max-width: 575px) {
    font-size: 18px;
    padding: 24px;
    border-bottom: 1px solid $alto;
    opacity: 1;
  }

  &__content {
    flex: 1 1 auto;
    width: 0;

    &__description {
      display: none;

      @media screen and (max-width: 575px) {
        display: block;
        font-size: 14px;
        font-weight: 300;
        margin-top: 8px;
        min-height: 14px;
      }
    }
  }

  &__caret {
    display: none;

    @media screen and (max-width: 575px) {
      display: block;
      background-image: url('/images/caret-right.svg');
      width: 36px;
      height: 36px;
      opacity: .5;
      background-size: contain;
      background-repeat: no-repeat;
      background-position: center;
    }
  }

  &--active {
    opacity: 1 !important;
  }
}

.tab-bar__grow-tab {
  flex-grow: 1;
}