Thanks to @takluyver for pointing this out
@ -472,7 +472,7 @@ class DOMWidget(Widget):
'bolder',
'lighter',
'initial',
'inherit', ''] + map(str, range(100,1000,100)),
'inherit', ''] + list(map(str, range(100,1000,100))),
default_value='', sync=True)
font_size = CUnicode(sync=True)
font_family = Unicode(sync=True)