diff --git a/core/toolbox.js b/core/toolbox.js
index 4047c729c..4c93e4c66 100644
--- a/core/toolbox.js
+++ b/core/toolbox.js
@@ -334,7 +334,7 @@ Blockly.Toolbox.prototype.syncTrees_ = function(treeIn, treeOut, pathToMedia) {
           }
         }
 
-        var styleName = childIn.getAttribute('style');
+        var styleName = childIn.getAttribute('categorystyle');
         var colour = childIn.getAttribute('colour');
 
         if (colour && styleName) {
diff --git a/tests/playground.html b/tests/playground.html
index 94bf7e2ac..66d4e935c 100644
--- a/tests/playground.html
+++ b/tests/playground.html
@@ -421,7 +421,7 @@ h1 {
   Variables category uses untyped variable blocks.
   See https://developers.google.com/blockly/guides/create-custom-blocks/variables#untyped_variable_blocks for more information. -->
   <xml id="toolbox-categories" style="display: none">
-    <category name="Logic" style="logic_category">
+    <category name="Logic" categorystyle="logic_category">
       <block type="controls_if"></block>
       <block type="logic_compare"></block>
       <block type="logic_operation"></block>
@@ -430,7 +430,7 @@ h1 {
       <block type="logic_null" disabled="true"></block>
       <block type="logic_ternary"></block>
     </category>
-    <category name="Loops" style="loop_category">
+    <category name="Loops" categorystyle="loop_category">
       <block type="controls_repeat_ext">
         <value name="TIMES">
           <shadow type="math_number">
@@ -460,7 +460,7 @@ h1 {
       <block type="controls_forEach"></block>
       <block type="controls_flow_statements"></block>
     </category>
-    <category name="Math" style="math_category">
+    <category name="Math" categorystyle="math_category">
       <block type="math_number" gap="32">
         <field name="NUM">123</field>
       </block>
@@ -561,7 +561,7 @@ h1 {
         </value>
       </block>
     </category>
-    <category name="Text" style="text_category">
+    <category name="Text" categorystyle="text_category">
       <block type="text"></block>
       <block type="text_join"></block>
       <block type="text_append">
@@ -663,7 +663,7 @@ h1 {
         </value>
       </block>
     </category>
-    <category name="Lists" style="list_category">
+    <category name="Lists" categorystyle="list_category">
       <block type="lists_create_with">
         <mutation items="0"></mutation>
       </block>
@@ -715,7 +715,7 @@ h1 {
       <block type="lists_sort"></block>
       <block type="lists_reverse"></block>
     </category>
-    <category name="Colour" style="colour_category">
+    <category name="Colour" categorystyle="colour_category">
       <block type="colour_picker"></block>
       <block type="colour_random"></block>
       <block type="colour_rgb">
@@ -754,15 +754,15 @@ h1 {
       </block>
     </category>
     <sep></sep>
-    <category name="Variables" style="variable_category" custom="VARIABLE"></category>
-    <category name="Functions" style="procedure_category" custom="PROCEDURE"></category>
+    <category name="Variables" categorystyle="variable_category" custom="VARIABLE"></category>
+    <category name="Functions" categorystyle="procedure_category" custom="PROCEDURE"></category>
   </xml>
 
   <!-- toolbox-categories-typed-variables has a category menu and an
   auto-closing flyout.  The Variables category uses typed variable blocks.
   See https://developers.google.com/blockly/guides/create-custom-blocks/variables#typed_variable_blocks for more information. -->
   <xml id="toolbox-categories-typed-variables" style="display: none">
-    <category name="Logic" style="logic_category">
+    <category name="Logic" categorystyle="logic_category">
       <block type="controls_if"></block>
       <block type="logic_compare"></block>
       <block type="logic_operation"></block>
@@ -771,7 +771,7 @@ h1 {
       <block type="logic_null" disabled="true"></block>
       <block type="logic_ternary"></block>
     </category>
-    <category name="Loops" style="loop_category">
+    <category name="Loops" categorystyle="loop_category">
       <block type="controls_repeat_ext">
         <value name="TIMES">
           <shadow type="math_number">
@@ -801,7 +801,7 @@ h1 {
       <block type="controls_forEach"></block>
       <block type="controls_flow_statements"></block>
     </category>
-    <category name="Math" style="math_category">
+    <category name="Math" categorystyle="math_category">
       <block type="math_number" gap="32">
         <field name="NUM">123</field>
       </block>
@@ -902,7 +902,7 @@ h1 {
         </value>
       </block>
     </category>
-    <category name="Text" style="text_category">
+    <category name="Text" categorystyle="text_category">
       <block type="text"></block>
       <block type="text_join"></block>
       <block type="text_append">
@@ -1004,7 +1004,7 @@ h1 {
         </value>
       </block>
     </category>
-    <category name="Lists" style="list_category">
+    <category name="Lists" categorystyle="list_category">
       <block type="lists_create_with">
         <mutation items="0"></mutation>
       </block>
@@ -1056,7 +1056,7 @@ h1 {
       <block type="lists_sort"></block>
       <block type="lists_reverse"></block>
     </category>
-    <category name="Colour" style="colour_category">
+    <category name="Colour" categorystyle="colour_category">
       <block type="colour_picker"></block>
       <block type="colour_random"></block>
       <block type="colour_rgb">
@@ -1095,8 +1095,8 @@ h1 {
       </block>
     </category>
     <sep></sep>
-    <category name="Variables" style="variable_category" custom="VARIABLE_DYNAMIC"></category>
-    <category name="Functions" style="procedure_category" custom="PROCEDURE"></category>
+    <category name="Variables" categorystyle="variable_category" custom="VARIABLE_DYNAMIC"></category>
+    <category name="Functions" categorystyle="procedure_category" custom="PROCEDURE"></category>
   </xml>
 
   <!-- toolbox-test-blocks has a category menu and an auto-closing flyout.