Edit in JSFiddle

#fizzbuzz { counter-reset: number; }
#fizzbuzz li { counter-increment: number; }
#fizzbuzz li::after { content: counter(number); }
#fizzbuzz li:nth-child(3n)::after { content:""; }
#fizzbuzz li:nth-child(3n)::before { content:"Fizz"; }
#fizzbuzz li:nth-child(5n)::after { content:"Buzz"; }
<ul id="fizzbuzz">
</ul>
var li = new Array();
for (i = 1; i <= 100; i++) {
    li.push("<li></li>");
}
document.getElementById("fizzbuzz").innerHTML = li.join("");