&&
works by stringing-together multiple selectors like-so:
<div class="class1 class2"></div>
div.class1.class2
{
/* foo */
}
Another example:
<input type="radio" class="class1" />
input[type="radio"].class1
{
/* foo */
}
||
works by separating multiple selectors with commas like-so:
<div class="class1"></div>
<div class="class2"></div>
div.class1,
div.class2
{
/* foo */
}