tab-group[split-view-group] {
    flex-direction: column;
    padding: 2px 2px !important;
    position: relative;

    &::after {
        content: '';
        width: 3px;
        height: calc(100% - 8px);
        background-color: var(--tab-selected-bgcolor);
        position: absolute;
        left: 2px;
        top: 50%;
        transform: translateY(-50%);
        border-radius: 2px
    }

    &:hover, &:has(> tab:is([visuallyselected], [multiselected])){
        &::after{
            width: 0;
        }
    }
}

tab-group[split-view-group] {
    & > .tabbrowser-tab {
        &:not(:last-child)::after {
            width: 0 !important;
            height: 0 !important;
        }
    }
}