diff --git a/src/index.html b/src/index.html
index c66a446..8e36042 100644
--- a/src/index.html
+++ b/src/index.html
@@ -46,7 +46,7 @@ <h1 id="main-header" class="navbar-brand">
                 </div>
             </nav>
             <p>${t('description')}</p>
-            <button class="btn btn-primary d-block mx-auto m-3" autofocus id="start-button" onclick="startSession()">
+            <button class="btn btn-primary form-control fs-5 d-block mx-auto m-3" autofocus id="start-button" onclick="startSession()">
                 <svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="currentColor" class="bi bi-play" viewBox="0 0 16 16">
                     <path d="M10.804 8 5 4.633v6.734zm.792-.696a.802.802 0 0 1 0 1.392l-6.363 3.692C4.713 12.69 4 12.345 4 11.692V4.308c0-.653.713-.998 1.233-.696z"/>
                 </svg>