JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="block info">
    <span class="class-span" id="idSpan" style="color: purple">Quelle est ma couleur ?</span>
  </div>
</div>

<hr>

<button id="Toggle">Afficher / Cacher</button>

CSS

span {
  color: blue !important;
}

#idSpan {
  color: red;
}

.block.info span {
  color: yellow;
}

.container .block.info span.class-span {
  color: green;
}

span.class-span {
  color: orange;
}

JavaScript

document.getElementById("idSpan").style.display = "none";

document.querySelector("#Toggle").addEventListener("click", function() {
  var display = "none";
  var span = document.getElementById("idSpan")
  
  if (span.style.display == "none") {
  	display = "block"
  }
  
  span.style.display = display
});