Styling nested, unordered list

Hi,

I have a pair of nested, unordered lists like the following:

I want the outer list to be styled without a list item marker {list-style-type: none} but I do want to apply {list-style-type: disk} to the inner list items.

This declaration doesn't work:

.bullets ul li {
list-style-type: none;
}
.bullets ul li ul li a {
list-style-type: disk;
}

What is the proper syntax? Also, any recommended writeups that describe how styles are applied to elements, (hopefully with lots of examples!)

Thanks in advance