Shaarli Related Plugin Dark CSS (Ref: https://github.com/ilesinge/shaarli-related/blob/master/related/related.css)

related.css

.related_links {
        color: #bbb;
    background: #333;
    z-index: 1000;
    padding: 5px;
    font-size: 0.8em;
    box-shadow: 0 -1px 0 #e5e5e5,0 0 2px rgba(0,0,0,.12),0 2px 4px rgba(0,0,0,.24);
    border-radius: 2px;
    list-style-type: none;
    margin: 0;
    overflow-wrap: break-word;
}
#related_popin {
    position: absolute;
    width:500px;
    max-width:50%;
}
#related_popin .link-title {
    display: inline;
}
#related_popin .linklist-item-title {
    background: none;
}
#related_popin .linktitle {
    font-size: inherit;
}