css class and id selector
Select an element with the ID "id" and the class "class":
#id.class {
}
example:
<div>
<strong id="id" class="class">
Foobar
</strong>
<strong class="class">
Foobar
</strong>
</div>
=> Will select the first <strong> element
Select all elements with the class "class",
which are decendents of a element with an ID of "id":
#id .class {
}
example:
<div id="id">
<strong class="class">Foobar</strong>
</div>
=> Will select the <strong> element