Html

<!DOCTYPE html>
<html>
<title>HTML</title>
<meta charset="utf-8" />
<link rel="stylesheet" href="index.css">
<head>
</head>
<body>
   <div class="name">
      <button>SkyMania</button>
   </div>
   <div class="nav"></div>
   <div class="info">
     <button>Info</button>
   </div>
   <div class="accueil">
      <button>Accueil</button>
   </div>
   <div class="dialog hidden">
      <label id="info">SkyMania est un serveur Minecraft SkyBlock accesible à la version 1.8</label>
   </div>
   <div class="boutique">
      <button>Boutique</button>
   </div>
   <script src="https://code.jquery.com/jquery-3.2.1.min.js">
   </script>

   <script>
      var info = document.querySelectorAll('.info');
      var dialog = document.querySelectorAll('.dialog');

      $('.info button').click(function(){
      dialog[0].classList.remove('hidden');
     });
     $('.accueil button').click(function(){
      dialog[0].classList.add('hidden');
     });
     $('.boutique button').click(function() {
      dialog[0].classList.add('hidden');
     });
   </script>
</body>
</html>