At our work the mighty rule for designing UI is “less is more”
I think its better to use that rule for reading the docs, and keep it as clean as possible.
To do that use this stylesheet
.tree-leaf .tree-expando.expanded {
/* opacity: 1.0; */
/* border-right: 1px solid #222; */
}
.tree-leaf .tree-expando.expanded {
/* opacity: 1.0; */
/* border-right: 1px solid #222; */
}
.tree-leaf .tree-expando {
/* border-radius: 50%; */
/* background: #ddd; */
/* width: .4rem; */
/* height: .4em; */
/* font-size: 1rem;*/
/* line-height: 1em; */
/* margin-top: 0.35em; */
/* border: 1px solid #222; */
/* opacity: 0.5; */
/* border-right: 1px solid #222; */
color: #9B4DCA;
}
.tree-leaf .tree-expando {
/* background: #ddd; */
/* border-radius: 2px; */
cursor: pointer;
float: left;
/* position: relative; */
/* text-align: center; */
/* width: 12px; */
}
the output is this:

I will fine tune this later
so its only:
.tree-leaf .tree-expando.expanded {}
.tree-leaf .tree-expando {
    color: #9B4DCA;
    cursor: pointer;
    float: left;
}
EDIT: oops a little to less here, update comming soon