Custom HTML broken in Look and Feel after saving invalid HTML

In the Administration->Look and Feel->Custom HTML, I've edited the Custom HTML and due to some broken tags I wasn't able to 'Save' the customization when I try editing it again. The save button no longer show up in edit mode.

You will need to remove all the customized HTML and run /admin/doeditcustomhtml.action on your Confluence instance. Please note that this operation will permanently remove the previous custom HTML.