Switch view/sort to fixed position

Close #1232

h/css/common.scss

@@ -1219,7 +1219,7 @@ h3.stream {
   @include single-transition(top, .25s);
   width: 100%;
   text-align: center;
-  position: absolute;
+  position: fixed;
   top: 29px;
   right: 0;
   z-index: 4;