Styling based on sibling count (http://lea.verou.me/2011/01/styling-children-based-on-their-number-with-css3/)

sibling-count.css

/* one item */
li:first-child:nth-last-child(1) {
	width: 100%;
}

/* two items */
li:first-child:nth-last-child(2),
li:first-child:nth-last-child(2) ~ li {
	width: 50%;
}

/* three items */
li:first-child:nth-last-child(3),
li:first-child:nth-last-child(3) ~ li {
	width: 33.3333%;
}

/* four items */
li:first-child:nth-last-child(4),
li:first-child:nth-last-child(4) ~ li {
	width: 25%;
}