HTML5とCSS3で文字を使わず「>」ボタンを作る方法

    <div id="a1">
        <div></div>
    </div>

#a1{
    position: relative;
    width: 60px;
    height: 60px;
    border: solid 1px black;
    border-radius: 30%;
    background-color: black;
}
#a1 > div{
    position: absolute;
    border-top: solid .15em white;
    border-right: solid .15em white;
    width: 30%;
    height: 30%;
    top:50%;
    left:45%;
    transform: translate(-50%, -50%) rotate(45deg);
}