Dark theme tweaks

* Fixes hourglasses
* Fix delivered status icon
* Other changes aiming for more consistency of visual structure
  between light and dark themes.
* Restores left pane header focus/transition effect.

stylesheets/android-dark.scss

@@ -10,18 +10,21 @@ $text-dark: #CCCCCC;
     border-color: $grey-dark;
   }
   #header {
-    background-color: $grey-dark;
-    color: $text-dark;
+    background-color: $blue;
+    color: white;
     transition: background-color 0.5s;
     &.inactive {
       background-color: $grey-dark;
       color: $text-dark;
     }
   }
-  .message-detail, .message-container, .conversation, .modal .content,
-  .discussion-container, .attachment-previews {
+  .message-detail, .message-container, .conversation,
+  .discussion-container {
     background-color: $grey-dark_l3;
   }
+  .modal .content {
+    background-color: $grey-dark;
+  }
   .lightbox .content {
     background-color: rgba(0, 0, 0, 0);
   }
@@ -37,9 +40,9 @@ $text-dark: #CCCCCC;
     }
   }
   .flex {
-    background-color: $grey-dark_l2;
+    background-color: $grey-dark_l3;
     .send-message {
-      background-color: $grey-dark_l2;
+      background-color: $grey-dark_l3;
       color: $text-dark;
     }
   }
@@ -73,6 +76,10 @@ $text-dark: #CCCCCC;
     display: inline-block;
     @include color-svg('/images/check.svg', white);
   }
+  .delivered .status {
+    display: inline-block;
+    @include color-svg('/images/double-check.svg', white);
+  }
   .paperclip:before {
     content: '';
     display: inline-block;
@@ -82,7 +89,7 @@ $text-dark: #CCCCCC;
     transform: rotateZ(-45deg);
   }
   .scrollable {
-    background-color: $grey-dark_l3;
+    background-color: $grey-dark_l2;
     .conversation-list-item {
       background-color: $grey-dark_l3;
       color: $text-dark;
@@ -91,11 +98,18 @@ $text-dark: #CCCCCC;
   .bottom-bar {
     min-height: 10px;
     background-color: $grey-dark_l2;
+    form.send {
+      background: $grey-dark_l3;
+    }
   }
   .search {
-    background-color: $grey-dark_l2;
+    background-color: $grey-dark_l3;
     border-color: $grey-dark_l2;
     @include invert-text-color;
+    &::-webkit-search-cancel-button {
+      background: url('/images/x_white.svg') no-repeat center;
+      background-size: cover;
+    }
   }
   .bubble {
     padding: 9px 12px;
@@ -106,9 +120,13 @@ $text-dark: #CCCCCC;
   .outgoing .bubble {
     background-color: $grey-dark;
     @include invert-text-color;
+    color: $text-dark;
   }
-  .outgoing .hourglass, .incoming .hourglass {
-    @include hourglass(#000);
+  .outgoing .hourglass {
+    @include hourglass(#999);
+  }
+  .incoming .hourglass {
+    @include hourglass(#fff);
   }
 
   .incoming .bubble {
@@ -130,17 +148,12 @@ $text-dark: #CCCCCC;
   button.back {
     @include header-icon-white('/images/back.svg');
   }
-  button.grey {
-    background-color: $grey-dark;
-    color: $text-dark;
-    border-color: $grey-dark_l2;
-  }
 
   ::-webkit-scrollbar-thumb {
-    background: rgba(120,120,120,0.15);
+    background: rgba(255,255,255,0.15);
 
     &:hover {
-      background: rgba(120,120,120,0.25);
+      background: rgba(255,255,255,0.25);
     }
   }
   ::-webkit-scrollbar-track {