Fix z-index conflict between aside and sidebar in mobile view (#3282)

Author: aqibshabir

packages/typescriptlang-org/src/templates/documentation.scss

@@ -81,7 +81,7 @@
       position: relative;
       top: 0;
       width: 100%;
-      z-index: 1000;
+      z-index: 98;
       margin-left: 0;
       order: 1;
     }