diff --git a/core/theme/classic.js b/core/theme/classic.js
index e88a6f25d..e4ab93e85 100644
--- a/core/theme/classic.js
+++ b/core/theme/classic.js
@@ -20,10 +20,7 @@ goog.module('Blockly.Themes.Classic');
 const Theme = goog.require('Blockly.Theme');
 
 
-// Temporary holding object.
-let Classic = {};
-
-Classic.defaultBlockStyles = {
+let defaultBlockStyles = {
   'colour_blocks': {'colourPrimary': '20'},
   'list_blocks': {'colourPrimary': '260'},
   'logic_blocks': {'colourPrimary': '210'},
@@ -36,7 +33,7 @@ Classic.defaultBlockStyles = {
   'hat_blocks': {'colourPrimary': '330', 'hat': 'cap'}
 };
 
-Classic.categoryStyles = {
+let categoryStyles = {
   'colour_category': {'colour': '20'},
   'list_category': {'colour': '260'},
   'logic_category': {'colour': '210'},
@@ -48,7 +45,13 @@ Classic.categoryStyles = {
   'variable_dynamic_category': {'colour': '310'}
 };
 
-Classic =
-    new Theme('classic', Classic.defaultBlockStyles, Classic.categoryStyles);
+/**
+ * Classic theme.
+ * Contains multi-coloured border to create shadow effect.
+ * @type {Theme}
+ * @alias Blockly.Themes.Classic
+ */
+const Classic =
+    new Theme('classic', defaultBlockStyles, categoryStyles);
 
 exports = Classic;
diff --git a/core/theme/zelos.js b/core/theme/zelos.js
index 5b87e23ef..edd321c0a 100644
--- a/core/theme/zelos.js
+++ b/core/theme/zelos.js
@@ -18,10 +18,7 @@ goog.module('Blockly.Themes.Zelos');
 const Theme = goog.require('Blockly.Theme');
 
 
-// Temporary holding object.
-let Zelos = {};
-
-Zelos.defaultBlockStyles = {
+let defaultBlockStyles = {
   'colour_blocks': {
     'colourPrimary': '#CF63CF',
     'colourSecondary': '#C94FC9',
@@ -75,7 +72,7 @@ Zelos.defaultBlockStyles = {
   }
 };
 
-Zelos.categoryStyles = {
+let categoryStyles = {
   'colour_category': {'colour': '#CF63CF'},
   'list_category': {'colour': '#9966FF'},
   'logic_category': {'colour': '#4C97FF'},
@@ -87,6 +84,11 @@ Zelos.categoryStyles = {
   'variable_dynamic_category': {'colour': '#FF8C1A'}
 };
 
-Zelos = new Theme('zelos', Zelos.defaultBlockStyles, Zelos.categoryStyles);
+/**
+ * Zelos theme.
+ * @type {Theme}
+ * @alias Blockly.Themes.Zelos
+ */
+const Zelos = new Theme('zelos', defaultBlockStyles, categoryStyles);
 
 exports = Zelos;