*{
    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;
}
.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;
}