Put the keyboard focus reticle back on top of diffs

Summary:
Fixes T10954. This got hidden underneath things at some point.

Use `pointer-events: none` to make the mouse ignore the element so that hover/select/edit/click still work "through" the element.

Design could probably be improved here, maybe I'll make it more-visible when you press {key n} and then have it fade quickly so it kind of gets out of your way once you find the block you want to read.

Test Plan: {F4921746}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10954

Differential Revision: https://secure.phabricator.com/D17784

webroot/rsrc/css/application/base/standard-page-view.css

@@ -61,9 +61,10 @@ body.white-background {
 }
 
 .keyboard-focus-focus-reticle {
-  background: #ffffd3;
+  background: rgba(255, 255, 211, 0.15);
   position: absolute;
-  border: 1px solid #999900;
+  border: 1px solid {$yellow};
+  pointer-events: none;
 }
 
 a.handle-status-closed {

webroot/rsrc/css/core/z-index.css

@@ -2,16 +2,16 @@
  * @provides phabricator-zindex-css
  */
 
-.keyboard-focus-focus-reticle {
-  z-index: 1;
-}
-
 .device .phabricator-action-list-view.phabricator-action-list-toggle,
 .device-desktop .phui-document-content
   .phabricator-action-list-view.phabricator-action-list-toggle {
   z-index: 1;
 }
 
+.keyboard-focus-focus-reticle {
+  z-index: 2;
+}
+
 .device-desktop .phui-timeline-minor-event .phui-timeline-image {
   z-index: 2;
 }