Fix theme path and include theme vars only

Author: janodvarko

data/markup-tooltip.js

@@ -41,6 +41,7 @@ function initialize(data) {
   // 'devtools.theme' preference, so make sure to properly
   // convert it into class name.
   document.body.classList.add("theme-" + data.theme);
+  document.documentElement.classList.add("theme-" + data.theme);
 
   // Get content ready for rendering.
   var store = new GripStore();

lib/data-tooltip.js

@@ -116,9 +116,15 @@ DataTooltip.prototype =
       let data = JSON.stringify(this.jQueryData);
       let theme = Services.prefs.getCharPref("devtools.theme");
 
+      // xxxHonza: can be removed as soon as Fx44 is the
+      // minimum requirement.
       loadSheet(win, "chrome://browser/skin/devtools/" + theme +
         "-theme.css", "author");
 
+      // Theme paths have changed in Fx44. Also, it should be enough
+      // to included only them variables.
+      loadSheet(win, "resource://devtools/client/themes/variables.css", "author");
+
       // The tooltip is opened for clicked jQuery data, so pass
       // it in together with the current active theme.
       let input = Content.cloneIntoContentScope(win, {