Merge pull request #318 from ckeditor/t/315

Fix: Fixed sticky panel `z-index` so it's correctly rendered above images (or other relatively positioned elements). Closes #315.

Author: Reinmar

theme/components/panel/stickypanel.scss

@@ -4,6 +4,7 @@
 @include ck-editor {
 	.ck-sticky-panel {
 		&.ck-sticky-panel_sticky {
+			z-index: ck-z( 'modal' ); // #315
 			position: fixed;
 			top: 0;