Oh, thank you for sharing. Also, I tested out the snipped and it is really nice. My css for relationship lines looks as follows:
/* folder relationship lines */
.nav-folder-children .nav-folder-children {
margin-left: 20px;
padding-left: 0;
border-left: 1px solid rgba(118,158,165,0.2);
border-radius: 4px;
transition:all 0.5s ease-in-out;
}
.nav-folder-children .nav-folder-children:hover {
border-left-color: rgba(118,158,165,0.4);
}
/* bullet point relationship lines */
.cm-hmd-list-indent .cm-tab, ul ul { position: relative; }
.cm-hmd-list-indent .cm-tab::before, ul ul::before {
content:'';
border-left: 1px solid rgba(0, 122, 255, 0.25);
position: absolute;
}
.cm-hmd-list-indent .cm-tab::before { left: 0; top: -5px; bottom: -4px;
}
ul ul::before { left: -11px; top: 0; bottom: 0;
}
I should mention, that it is - what funny coincidence - taken from @EleanorKonik. (But I can’t remember when and from where exactly
) Also, I should mention that the above shared screenshots stem from Light Theme in RemNote, done by eustachio.
Anyway - a next question. Now, how do I insert the snippet into my css for relationship lines?
When I activate the snippet you shared and the css-file for relationship lines at the same time, it looks like this:
When I only activate the snippet you shared, some relationship lines are missing and it looks like this:
Otherwise it is pretty, awesomely sweet! 
Ok, maybe you can help me out on the short run? (For the future, I’ll definetly look into some css tutorials.)
And: Thanks!