. code has been updated in the first post to avoid unwanted highlights inside the linked refs block
. optionnal highlights for tree lines (needs a bit of tweaking if you’re using a custom theme, and lines are full height) - this would be better using javascript
result
code
/*--- highlight tree lines ---*/
/*--- tweak left: and top: offset to match yout theme */
.blocks-container > div:not(:first-child) .ls-block:focus-within > div:first-child .bullet:before{
content : "└─";
color:#f00;
display: inline-block;
left: -24px;
top: -6px;
width: 30px;
position: relative;
}
.ls-block > .block-children:focus-within {
border-left-color:#f00;
}