Add padding to preferences page

src/invidious/views/preferences.ecr

@@ -8,6 +8,7 @@ function update_value(element) {
 }
 </script>
 
+<div class="h-box">
     <form class="pure-form pure-form-aligned" action="/preferences?referer=<%= referer %>" method="post">
         <fieldset>
             <legend>Player preferences</legend>
@@ -77,3 +78,4 @@ function update_value(element) {
             </div>
         </fieldset>
     </form>
+</div>