Adds inverted accordion variation

src/definitions/modules/accordion.less

@@ -210,6 +210,12 @@
   width: 100%;
 }
 
+/*--------------
+     Inverted
+---------------*/
 
+.ui.inverted.accordion .title:not(.ui) {
+  color: @invertedTitleColor;
+}
 
 .loadUIOverrides();

src/themes/default/modules/accordion.variables

@@ -97,5 +97,6 @@
 @styledActiveChildTitleBackground: @styledActiveTitleBackground;
 @styledActiveChildTitleColor: @styledActiveTitleColor;
 
-
+/* Inverted */
+@invertedTitleColor: @invertedTextColor;