<details open>
<summary>title</summary>
<ul>
<li>item1</li>
<li>item2</li>
<li>item3</li>
<li>item4</li>
</ul>
</details>
.indent summary::marker {
content: '+ ';
}
.indent li {
display: flex;
align-items: center;
}
.indent li::before {
content: '';
width: 2em;
height: 1px;
background-color: #bdc3c7;
}
.indent[open] summary::marker {
content: '- ';
}
.indent[open] ul {
border-left: 1px solid #bdc3c7;
}