opera style tabs for firefox split view (firefox css)

userChrome.css

/* opera style split tabs */

.tab-split-view-container {
    /* remove default split view background */
    background: transparent !important;
    .tabbrowser-tab {
        & .tab-background {
            /* both tabs need to have a matching background */
            background:var(--tab-selected-bgcolor) !important;
            box-shadow: none !important; /* shadow clashes with opera style */
        }
        & .tab-label[selected] {
            color:AccentColor;
        }
        &:first-child {
            /* this produces the bridge between tabs */
            &::after {
                content:"";
                background:var(--tab-selected-bgcolor); /* matching background */
                min-width:10px; /* seperation length */
                height:40%; /* how thick */
                margin: auto; /* easy centering */
                border-radius: 2px;
            }
        }
    }
}