Hide "Change the Look" Menu Item

In the "Cog" wheel settings menu, how can I remove the item "Change the look" for everyone? I tried the following CSS with no success:

#ctl00_PlaceHolderMain_Customization_RptControls_Theme {
    display:none;
}

I can hide it by ID, but the ID changes depending on where you are, so this is no good

#mpl_0_7_Anchor {
    display:none;
}

jQuery would even be acceptable but I have no success targeting the span element:

$("span:contains('Change the look')").hide();

Am I close?