.check{
    display: none;
}
.label{
    background: #666;
    color: #fff;
    display: block;
    margin-bottom: 1px;
    padding: 10px;
    position:relative;
    width:300px;
}
.content{
    border: 1px solid #eee;
    height: 0;
    opacity: 0;
    padding: 0 10px;
    transition: .5s; 
    width:300px;
}
.content p{
    margin:0;
}
.check:checked + .label + .content{
    height: 50px;
    opacity: 1;
    padding: 10px;
}
/* 三角形 */
.label:after{
    content:"";
    width: 0;
    height: 0;
    border-style: solid;
    border-width: 13px 7px 0 7px;
    border-color: #fff transparent transparent transparent;
    position: absolute;
    right: 1em;
    top: 15px;
}
.check:checked + .label:after{
    content:"";
    width: 0;
    height: 0;
    border-style: solid;
    border-width: 0 7px 13px 7px;
    border-color: transparent transparent #fff transparent;
}