Witam. Jezeli css to :target
<a href="#content"><button>rozwiń opis</button></a>
<div class="content" id="content">Opis produktu</div>
<p>content</p>
body{
background-color: #000;
color: #fff;
}
.content{
height: 0;
overflow: hidden;
transition: all 1s;
}
:target {
height: 18px;
}