JSFiddle - React, Tailwind, and code Playground

HTML

<a id="spoiler" href="#" onclick="spoiler()">+</a>
<div id="hidden_block">
    <audio controls>Тег аудио не поддерживается вашим браузером</audio>
</div>

CSS

a#spoiler {
    text-decoration:none;
    font-size:30px;
}

div#hidden_block {
    background:greenyellow;
    width:300px;
    padding:10px;
    display:none;
}

JavaScript

var d = document;

function spoiler() {
    
    var hidden_block = d.getElementById('hidden_block');
    var a_anchor = d.getElementById('spoiler');
    
    if(hidden_block.style.display == 'block') {
        hidden_block.style.display = '';
        a_anchor.innerHTML = '+';
    }
    
    else {
        hidden_block.style.display = 'block';
        a_anchor.innerHTML = '-';
    }
    
}