I've used the custom UI editor to try to add an icon my a button on a new tab.
The new button is added but the icon is not displayed on it.
The contents of the customUI folder is:
_rels\customUI.xml.rels:
< xml version="1.0" encoding="utf-8" >
<Relationship Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/image" Target="images/Green_Atom.png" Id="Green_Atom" />
</Relationships>
customUI.xml:
This seems correct and no error message is raised, so why is it not displayed