Sticky editor with preview on?

[john.edw_gmail.com]

When preview mode is engage the parent (.tc-tiddler-preview) of .tc-editor-toolbar has overflow set to auto which breaks sticky?

removing overflow: auto allows the toolbar to sticky in either mode, hwoever I don’t know what it might break.

.tc-tiddler-preview {
  overflow: unset;
}
.tc-editor-toolbar {
	position: -webkit-sticky;
	position: -moz-sticky;
	position: -o-sticky;
	position: -ms-sticky;
	position: sticky;
	top: 40px;
	background: #f3f3f3;
	z-index: 500;
}