style(web): cap ranking search box at 320px

reaction_board/web/static/style.css

@@ -538,6 +538,7 @@ h1, h2, h3, p { margin: 0; }
   display: flex;
   flex: 1 1 120px;
   min-width: 96px;
+  max-width: 320px;
   margin-left: auto;
 }
 .search-box { position: relative; display: flex; align-items: center; width: 100%; }