initial stab at an official dark theme via the magic of SASS.

SVGs are all broken, and some of the more exotic colours haven't been updated. There's been no attempt to use SASS to remove duplication from the CSS yet.
no attempt to switch it at runtime yet.

src/skins/vector/css/themes/_base.scss

@@ -0,0 +1,68 @@
+
+
+// typical text (dark-on-white in light skin)
+$primary-fg-color: #454545;
+$primary-bg-color: #ffffff;
+
+// used for dialog box text
+$light-fg-color: #747474;
+
+// button UI (white-on-green in light skin)
+$accent-fg-color: #ffffff;
+$accent-color: #76CFA6;
+
+// red warning colour
+$warning-color: #ff0064;
+
+// left-panel style muted accent color
+$secondary-accent-color: #eaf5f0;
+
+// used by AddressSelector
+$selected-color: #eaf5f0;
+
+// selected for hoverover & selected event tiles
+$event-selected-color: #f7f7f7;
+
+// used for the hairline dividers in RoomView
+$primary-hairline-color: #e5e5e5;
+
+// used for the border of input text fields
+$input-border-color: #f0f0f0;
+
+// apart from login forms, which have stronger border
+$strong-input-border-color: #c7c7c7;
+
+// context menus
+$menu-border-color: rgba(187, 187, 187, 0.5);
+$menu-bg-color: #f6f6f6;
+
+$avatar-initial-color: #ffffff;
+
+// ********************
+
+$roomtile-name-color: rgba(69, 69, 69, 0.8);
+$roomtile-selected-bg-color: rgba(255, 255, 255, 0.8);
+
+$roomsublist-label-fg-color: #3d3b39;
+$roomsublist-label-bg-color: #d3efe1;
+
+// ********************
+
+// event tile lifecycle
+$event-encrypting-color: #abddbc;
+$event-sending-color: #ddd;
+$event-notsent-color: #f44;
+
+// event timestamp
+$event-timestamp-color: #acacac;
+
+// e2e
+$e2e-verified-color: #76cfa5; // N.B. *NOT* the same as $accent-color
+$e2e-unverified-color: #e8bf37;
+$e2e-warning-color: #ba6363;
+
+// ********************
+
+$lightbox-bg-color: #454545;
+$lightbox-fg-color: #ffffff;
+$lightbox-border-color: #ffffff;