Simplify insertion of "Join Room" button

   }
   document.documentElement.className = currentColorMode
 
-  const joinButton = document.createElement('button')
-  joinButton.innerHTML = 'Join Room'
-  joinButton.id = 'join'
   const navDiv = document.querySelector("body > nav div")
-  navDiv.insertBefore(joinButton, navDiv.firstChild);
+  navDiv.innerHTML = `<button id=join>Join Room</button>` + navDiv.innerHTML
 
   microphoneStatus('off')
   colormode.onmouseup = toggleColorMode