diff --git a/core/inject.js b/core/inject.js
index be46c684c..b64576bc4 100644
--- a/core/inject.js
+++ b/core/inject.js
@@ -163,6 +163,10 @@ Blockly.createMainWorkspace_ = function(svg, options, blockDragSurface,
   mainWorkspace.scale = options.zoomOptions.startScale;
   svg.appendChild(mainWorkspace.createDom('blocklyMainBackground'));
 
+  // Set the theme name on the injection div.
+  Blockly.utils.dom.addClass(mainWorkspace.getInjectionDiv(),
+      mainWorkspace.getTheme().name + '-theme');
+
   if (!options.hasCategories && options.languageTree) {
     // Add flyout as an <svg> that is a sibling of the workspace svg.
     var flyout = mainWorkspace.addFlyout('svg');
diff --git a/core/options.js b/core/options.js
index c84a4264e..d2596c392 100644
--- a/core/options.js
+++ b/core/options.js
@@ -286,7 +286,7 @@ Blockly.Options.parseThemeOptions_ = function(options) {
   if (theme instanceof Blockly.Theme) {
     return /** @type {!Blockly.Theme} */ (theme);
   }
-  return new Blockly.Theme(
+  return new Blockly.Theme('builtin',
       theme['blockStyles'], theme['categoryStyles'], theme['componentStyles']);
 };
 
diff --git a/core/theme.js b/core/theme.js
index 52c723322..eab7a856e 100644
--- a/core/theme.js
+++ b/core/theme.js
@@ -28,6 +28,7 @@ goog.require('Blockly.utils.colour');
 
 /**
  * Class for a theme.
+ * @param {string} name Theme name.
  * @param {!Object.<string, Blockly.Theme.BlockStyle>} blockStyles A map from
  *     style names (strings) to objects with style attributes for blocks.
  * @param {!Object.<string, Blockly.Theme.CategoryStyle>} categoryStyles A map
@@ -37,7 +38,15 @@ goog.require('Blockly.utils.colour');
  *     names to style value.
  * @constructor
  */
-Blockly.Theme = function(blockStyles, categoryStyles, opt_componentStyles) {
+Blockly.Theme = function(name, blockStyles, categoryStyles,
+    opt_componentStyles) {
+
+  /**
+   * The theme name. This can be used to reference a specific theme in CSS.
+   * @type {string}
+   * @package
+   */
+  this.name = name;
   /**
    * The block styles map.
    * @type {!Object.<string, !Blockly.Theme.BlockStyle>}
diff --git a/core/theme/classic.js b/core/theme/classic.js
index b84057700..b39836de4 100644
--- a/core/theme/classic.js
+++ b/core/theme/classic.js
@@ -94,5 +94,5 @@ Blockly.Themes.Classic.categoryStyles = {
 };
 
 Blockly.Themes.Classic =
-    new Blockly.Theme(Blockly.Themes.Classic.defaultBlockStyles,
+    new Blockly.Theme('classic', Blockly.Themes.Classic.defaultBlockStyles,
         Blockly.Themes.Classic.categoryStyles);
diff --git a/core/theme/dark.js b/core/theme/dark.js
index 2aff84c02..7f4dad583 100644
--- a/core/theme/dark.js
+++ b/core/theme/dark.js
@@ -23,6 +23,7 @@
 
 goog.provide('Blockly.Themes.Dark');
 
+goog.require('Blockly.Css');
 goog.require('Blockly.Theme');
 
 
@@ -115,7 +116,7 @@ Blockly.Themes.Dark.categoryStyles = {
 
 // This style is still being fleshed out and may change.
 Blockly.Themes.Dark =
-    new Blockly.Theme(Blockly.Themes.Dark.defaultBlockStyles,
+    new Blockly.Theme('dark', Blockly.Themes.Dark.defaultBlockStyles,
         Blockly.Themes.Dark.categoryStyles);
 
 Blockly.Themes.Dark.setComponentStyle('workspace', '#1e1e1e');
@@ -126,3 +127,14 @@ Blockly.Themes.Dark.setComponentStyle('flyoutText', '#ccc');
 Blockly.Themes.Dark.setComponentStyle('flyoutOpacity', 1);
 Blockly.Themes.Dark.setComponentStyle('scrollbar', '#797979');
 Blockly.Themes.Dark.setComponentStyle('scrollbarOpacity', 0.4);
+
+/**
+ * CSS for the dark theme.
+ */
+Blockly.Css.register([
+  /* eslint-disable indent */
+  '.dark-theme .blocklyTreeRow:not(.blocklyTreeSelected):hover {',
+    'background-color: #2a2d2e;',
+  '}',
+  /* eslint-enable indent */
+]);
diff --git a/core/theme/deuteranopia.js b/core/theme/deuteranopia.js
index dc6d2e21f..dbd1bfbab 100644
--- a/core/theme/deuteranopia.js
+++ b/core/theme/deuteranopia.js
@@ -110,5 +110,6 @@ Blockly.Themes.Deuteranopia.categoryStyles = {
 };
 
 Blockly.Themes.Deuteranopia =
-    new Blockly.Theme(Blockly.Themes.Deuteranopia.defaultBlockStyles,
+    new Blockly.Theme('deuteranopia',
+        Blockly.Themes.Deuteranopia.defaultBlockStyles,
         Blockly.Themes.Deuteranopia.categoryStyles);
diff --git a/core/theme/highcontrast.js b/core/theme/highcontrast.js
index 449619a6d..3f2c15850 100644
--- a/core/theme/highcontrast.js
+++ b/core/theme/highcontrast.js
@@ -115,5 +115,6 @@ Blockly.Themes.HighContrast.categoryStyles = {
 
 // This style is still being fleshed out and may change.
 Blockly.Themes.HighContrast =
-    new Blockly.Theme(Blockly.Themes.HighContrast.defaultBlockStyles,
+    new Blockly.Theme('highcontrast',
+        Blockly.Themes.HighContrast.defaultBlockStyles,
         Blockly.Themes.HighContrast.categoryStyles);
diff --git a/core/theme/modern.js b/core/theme/modern.js
index 09e892dba..9d6cc6afd 100644
--- a/core/theme/modern.js
+++ b/core/theme/modern.js
@@ -115,5 +115,5 @@ Blockly.Themes.Modern.categoryStyles = {
 
 // This style is still being fleshed out and may change.
 Blockly.Themes.Modern =
-    new Blockly.Theme(Blockly.Themes.Modern.defaultBlockStyles,
+    new Blockly.Theme('modern', Blockly.Themes.Modern.defaultBlockStyles,
         Blockly.Themes.Modern.categoryStyles);
diff --git a/core/theme/tritanopia.js b/core/theme/tritanopia.js
index c12fec728..d90d86aa0 100644
--- a/core/theme/tritanopia.js
+++ b/core/theme/tritanopia.js
@@ -109,5 +109,6 @@ Blockly.Themes.Tritanopia.categoryStyles = {
 };
 
 Blockly.Themes.Tritanopia =
-    new Blockly.Theme(Blockly.Themes.Tritanopia.defaultBlockStyles,
+    new Blockly.Theme('tritanopia',
+        Blockly.Themes.Tritanopia.defaultBlockStyles,
         Blockly.Themes.Tritanopia.categoryStyles);
diff --git a/core/theme_manager.js b/core/theme_manager.js
index 3d6e09d7e..bf012b4d4 100644
--- a/core/theme_manager.js
+++ b/core/theme_manager.js
@@ -30,11 +30,19 @@ goog.require('Blockly.Theme');
 
 /**
  * Class for storing and updating a workspace's theme and UI components.
+ * @param {!Blockly.WorkspaceSvg} workspace The main workspace.
  * @param {!Blockly.Theme} theme The workspace theme.
  * @constructor
  * @package
  */
-Blockly.ThemeManager = function(theme) {
+Blockly.ThemeManager = function(workspace, theme) {
+
+  /**
+   * The main workspace.
+   * @type {!Blockly.WorkspaceSvg}
+   * @private
+   */
+  this.workspace_ = workspace;
 
   /**
    * The Blockly theme to use.
@@ -87,8 +95,18 @@ Blockly.ThemeManager.prototype.setTheme = function(theme) {
     return;
   }
 
+  var prevTheme = this.theme_;
   this.theme_ = theme;
 
+  // Set the theme name onto the injection div.
+  var injectionDiv = this.workspace_.getInjectionDiv();
+  if (injectionDiv) {
+    if (prevTheme) {
+      Blockly.utils.dom.removeClass(injectionDiv, prevTheme.name + '-theme');
+    }
+    Blockly.utils.dom.addClass(injectionDiv, this.theme_.name + '-theme');
+  }
+
   // Refresh all subscribed workspaces.
   for (var i = 0, workspace; (workspace = this.subscribedWorkspaces_[i]); i++) {
     workspace.refreshTheme();
diff --git a/core/workspace_svg.js b/core/workspace_svg.js
index 7a8034026..01909a3d0 100644
--- a/core/workspace_svg.js
+++ b/core/workspace_svg.js
@@ -143,7 +143,8 @@ Blockly.WorkspaceSvg = function(options,
    */
   this.themeManager_ = this.options.parentWorkspace ?
       this.options.parentWorkspace.getThemeManager() :
-      new Blockly.ThemeManager(this.options.theme || Blockly.Themes.Classic);
+      new Blockly.ThemeManager(this,
+          this.options.theme || Blockly.Themes.Classic);
 
   /**
    * The block renderer used for rendering blocks on this workspace.
diff --git a/tests/mocha/block_test.js b/tests/mocha/block_test.js
index b01e96989..80dca0974 100644
--- a/tests/mocha/block_test.js
+++ b/tests/mocha/block_test.js
@@ -1277,7 +1277,7 @@ suite('Blocks', function() {
         this.block = Blockly.Xml.domToBlock(Blockly.Xml.textToDom(
             '<block type="empty_block"/>'
         ), this.workspace);
-        this.workspace.setTheme(new Blockly.Theme({
+        this.workspace.setTheme(new Blockly.Theme('test', {
           "styleOne" : {
             "colourPrimary": "#000000",
             "colourSecondary": "#999999",
diff --git a/tests/mocha/theme_test.js b/tests/mocha/theme_test.js
index e6d5f7592..15f62686a 100644
--- a/tests/mocha/theme_test.js
+++ b/tests/mocha/theme_test.js
@@ -84,27 +84,27 @@ suite('Theme', function() {
   }
 
   test('Set All BlockStyles', function() {
-    var theme = new Blockly.Theme(createBlockStyles());
+    var theme = new Blockly.Theme('test', createBlockStyles());
     stringifyAndCompare(createBlockStyles(), theme.blockStyles_);
     theme.setAllBlockStyles(createMultipleBlockStyles());
     stringifyAndCompare(createMultipleBlockStyles(), theme.blockStyles_);
   });
 
   test('Get All BlockStyles', function() {
-    var theme = new Blockly.Theme(createMultipleBlockStyles());
+    var theme = new Blockly.Theme('test', createMultipleBlockStyles());
     var allBlocks = theme.getAllBlockStyles();
     stringifyAndCompare(createMultipleBlockStyles(), allBlocks);
   });
 
   test('Get BlockStyles', function() {
-    var theme = new Blockly.Theme(createBlockStyles());
+    var theme = new Blockly.Theme('test', createBlockStyles());
     var blockStyle = theme.getBlockStyle('styleOne');
 
     stringifyAndCompare(blockStyle, createBlockStyles().styleOne);
   });
 
   test('Set BlockStyle Update', function() {
-    var theme = new Blockly.Theme(createBlockStyles());
+    var theme = new Blockly.Theme('test', createBlockStyles());
     var blockStyle = createBlockStyles();
     blockStyle.styleOne.colourPrimary = '#00ff00';
 
@@ -114,7 +114,7 @@ suite('Theme', function() {
   });
 
   test('Set BlockStyle Add', function() {
-    var theme = new Blockly.Theme(createBlockStyles());
+    var theme = new Blockly.Theme('test', createBlockStyles());
     var blockStyle = createMultipleBlockStyles();
 
     theme.setBlockStyle('styleTwo', blockStyle.styleTwo);
diff --git a/tests/mocha/trashcan_test.js b/tests/mocha/trashcan_test.js
index 992e2cd91..7e0a0fd39 100644
--- a/tests/mocha/trashcan_test.js
+++ b/tests/mocha/trashcan_test.js
@@ -16,7 +16,6 @@
  */
 
 suite("Trashcan", function() {
-  var themeManager = new Blockly.ThemeManager(Blockly.Themes.Classic);
   var workspace = {
     addChangeListener: function(func) {
       this.listener = func;
@@ -24,13 +23,14 @@ suite("Trashcan", function() {
     triggerListener: function(event) {
       this.listener(event);
     },
-    getThemeManager: function() {
-      return themeManager;
-    },
     options: {
       maxTrashcanContents: Infinity
     }
   };
+  var themeManager = new Blockly.ThemeManager(workspace, Blockly.Themes.Classic);
+  workspace.getThemeManager = function() {
+    return themeManager;
+  };
   function sendDeleteEvent(xmlString) {
     var xml = Blockly.Xml.textToDom(
         '<xml xmlns="https://developers.google.com/blockly/xml">' +