hide the theme selector using CSS rather than ‹hidden›

resources/blogisek.js

@@ -30,5 +30,5 @@ if ( tsel ) {
             document.firstElementChild.dataset.theme = t;
         };
     }
-    tsel.hidden = false;
+    tsel.style = null;
 }

templates/nav.tt

 <div>
-<nav id=theme-selector hidden>
+<nav id=theme-selector style='visibility:hidden'>
     <button tabindex=0 data-theme=auto title='Motiv dle systému'></button>
     <button tabindex=0 data-theme=light title='Světlý'></button>
     <button tabindex=0 data-theme=dark title='Tmavý'></button>
     <button tabindex=0 data-theme=mixed title='Smíšený'></button>
 </nav>
-<script>document.getElementById('theme-selector').hidden=0;</script>
 <nav id=category-archives>
     <header>Škatulky</header>
     [%- INCLUDE archive a=categories %]