refactor(css): selektoren in main.css zusammenfassen

wwwroot/css/main.css

@@ -30,14 +30,10 @@ header {
   flex: 1;
 }
 
+header,
+.chat-page .page-content,
 .page-content:not(.chat-page .page-content) > * {
   width: var(--page-width);
   max-width: 100%;
   align-self: center;
 }
-
-.chat-page .page-content {
-  width: var(--page-width);
-  max-width: 100%;
-  align-self: center;
-}