Update page nav styles

Update the navigation styles to:
- Be full height
- Have a light grey background (slightly lighter than the PG header)
- Allow sections within the nav
- Allow for a selected item

This also increases the z-index of the footer so that when the nav is
fixed position, it doesn't overlap the footer.

Change-Id: I6cc3ec542c38d24b3f8b030abe3610b8aa838d1f
diff --git a/polygerrit-ui/app/elements/shared/gr-page-nav/gr-page-nav.html b/polygerrit-ui/app/elements/shared/gr-page-nav/gr-page-nav.html
index 5fa21e4..3209590 100644
--- a/polygerrit-ui/app/elements/shared/gr-page-nav/gr-page-nav.html
+++ b/polygerrit-ui/app/elements/shared/gr-page-nav/gr-page-nav.html
@@ -22,8 +22,10 @@
   <template>
     <style include="shared-styles">
       #nav {
+        background-color: #f5f5f5;
         border: 1px solid #eee;
         border-top: none;
+        height: 100%;
         position: absolute;
         top: 0;
         width: 14em;
@@ -32,7 +34,29 @@
         position: fixed;
       }
       #nav ::content ul {
-        margin: 1em 2em;
+        padding: 1em 0;
+      }
+      #nav ::content li {
+        border-bottom: 1px solid transparent;
+        border-top: 1px solid transparent;
+        padding: 0 2em;
+      }
+      #nav ::content li.sectionTitle {
+        padding: 0 2em 0 1.5em;
+      }
+      #nav ::content li.sectionTitle:not(:first-child) {
+        padding-top: 1em;
+      }
+      #nav ::content .title {
+        display: flex;
+        font-weight: bold;
+        margin: .4em 0;
+      }
+      #nav ::content .selected {
+        background-color: #fff;
+        border-bottom: 1px dotted #808080;
+        border-top: 1px dotted #808080;
+        font-weight: bold;
       }
       #nav ::content a {
         color: black;