Centering button with flex box (Safari)

HTML

<div>
    <button>
        <span>
            <span>Test</span>
            <span>Test</span>
        </span>
    </button>
    <p>
        <span>Test</span>
        <span>Test</span>
    </p>
</div>

CSS

div {
    display: flex;
    display: -webkit-flex;
    flex-direction: column;
    -webkit-flex-direction: column;
    width: 100%;
}

button > span, p {
    display: -webkit-flex;
    display: flex;
    -webkit-flex-direction: row;
    flex-direction: row;
    -webkit-justify-content: center;
    justify-content: center;
}