I have a css class like:
.foo { background-color: red; }
then I have a class specified for a list:
.list1 li { background-c
The above solutions aren't available if you don't have control over how 'foo' was defined.
So, if a JQuery solution is acceptable, just apply the original class to all instances of the new class/context. In this case:
$('.list li').addClass('foo')