Disini kita akan membuat menu accordion mengunakan HTML dan CSS, Ok langsung saja kita buat dulu code HTML seperti dibawah ini 
<!DOCTYPE html>
<html>
<head>
    <title>accordion</title>
    <link rel="stylesheet" type="text/css" href="css/style.css">
    <link href="https://stackpath.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css" rel="stylesheet">
</head>
<body>
<div class="middle">
    <div class="menu">
        <li class="item" id="profile">
            <a href="#profile" class="btn"><i class="fa fa-user" aria-hidden="true"></i></i>User</a>
            <div class="smenu">
                <a href="">Login</a>
                <a href="">Register</a>
            </div>
        </li>
 
 
        <li class="item" id="messages">
            <a href="#messages" class="btn"><i class="fa fa-commenting-o" aria-hidden="true"></i></i>Messages</a>
            <div class="smenu">
                <a href="">New</a>
                <a href="">Send</a>
                <a href="">Spam</a>
            </div>
        </li>
 
        <li class="item" id="setting">
            <a href="#setting" class="btn"><i class="fa fa-cog" aria-hidden="true"></i></i>Setting</a>
            <div class="smenu">
                <a href="">Password</a>
                <a href="">League</a>
            </div>
        </li>
        <li class="item">
            <a class="btn" href=""><i class="fa fa-sign-out" aria-hidden="true"></i>Logout</a>
        </li>
    </div>
</div>
</body>
</html>
Setelah selesai membuat code HTML kemudian buat fungsi accordion dengan css seperti contoh code dibawah ini 
*{
    margin: 0;
    padding: 0;
    font-family: sans-serif;
    list-style: none;
    text-decoration: none;
 
}
.middle{
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}
.menu{
    width: 300px;
    border-radius: 8px;
    overflow: hidden;
}
.item{
    border-top: 1px solid #2980b9;
    overflow: hidden;
}
.btn{
    display: block;
    padding: 16px 20px;
    background: #3498db;
    color: white;
}
.btn:before{
    content: '';
    position: absolute;
    width: 14px;
    height: 14px;
    background: #3498db;
    left: 20px;
    bottom: -7px;
    transform: rotate(45deg);
}
.btn i{
    margin-right: 10px;
}
.smenu{
    background: #34495e;
    overflow: hidden;
    transition: max-height 0.3s;
    max-height: 0;
}
.smenu a{
    display: block;
    padding: 16px 26px;
    color: white;
    font-size: 4px 0;
    position: relative;
}
.smenu a:before{
    content: '';
    position: absolute;
    width: 6px;
    height: 100%;
    background: #3498db;
    left: 0;
    top: 0;
    transition: 0.3s;
    opacity: 0;
}
.smenu a:hover:before{
    opacity: 1;
}
.item:target .smenu{
    max-height: 10em;
}
Semoga bermanfaat berikut adalah cara membuat menu accordion mengunakan HTML dan CSS