sanic/static/treeview.css

/* https://codepen.io/defims/pen/DBaVXM */

ul {
  float: left;
  clear: left;
  margin-left: .25em;
  padding: 0;
}

ul:before {
  content:"";
  position: absolute;
  z-index: 1;
  top:.25em;
  right:auto;
  bottom:0;
  left: 1.75em;
  margin: auto;
  /* border-right: dotted white .1em; */
  width: 0;
  height: auto;
}

ul:after {
  content: "-";
  position: absolute;
  z-index: 3;
  top: 0;
  left: -.5em;
  margin-left: .65em;
  margin-top: .15em;
  padding: 0;
  width: .8em;
  height: .8em;
  text-align: center;
  line-height: .7em;
  font-size: 1em;
}

ul > li {
  display: block;
  position: relative;
  float: left;
  clear: both;
  right:auto;
  padding-left: 1em;
  width:auto;
  text-align: center;
  color:white;
}

ul > li > input[type=checkbox] {
  display:block;
  position: absolute;
  float: left;
  z-index: 4;
  margin: 0 0 0 -1em;
  padding: 0;
  width:1em;
  height: 2em;
  font-size: 1em;
  opacity: 0;
  cursor: pointer;
}

ul > li > input[type=checkbox]:not(:checked)~ul:before {
  display: none;
}

ul > li > input[type=checkbox]:not(:checked)~ul:after {
  content: "+"
}

ul > li > input[type=checkbox]:not(:checked)~ul * {
  display: none;
}

ul > li > span {
  display: block;
  position: relative;
  float: left;
  z-index: 3;
  margin-left: .25em;
  padding-left: .25em;
}

ul > li > span:after {
  content: "";
  display: block;
  position: absolute;
  left:-1em;
  top:0;
  bottom:0;
  margin: auto .25em auto .25em;
  /* border-top: dotted white .1em; */
  width: .75em;
  height: 0;
}

ul > li:last-child:before {
  content: ""; display: block; position: absolute; z-index: 2;
  top:1em; left:0; bottom:-.25em;
  width:.75em; height:auto;
}

#tree {
  position: relative; font-family: "Georgia";
}

#tree:before {
  left:.5em;
}

#tree:after {
  display: none;
}

/* decoration */
ul, ul > li:last-child:before {
  background: transparent;
}

ul > li {
  background: transparent;
}

ul:after {
  background: linear-gradient(135deg, rgba(255,255,255,1), rgba(195,186,170,1));
  color: black;
  border:solid gray 1px;
  border-radius: .1em;
}

ul > li > span {
  border-radius: .25em;
  color: white;
}

ul > li > input[type=checkbox]~span:before {
  content:""; display: inline-block;
  margin: 0 .25em  0 0;
  width:1em; height: 1em; ;line-height: 1em;
  content: '\1F4C1';
  background-repeat:no-repeat;
  background-size:contain;
}

ul > li > input[type=checkbox]:checked~span:before {
  content: '\1F4C2';
}