.centered {
    position: fixed;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    /* bring your own prefixes */
}

a.button {
    -webkit-appearance: button;
    -moz-appearance: button;
    appearance: button;
    text-decoration: none;
    color: #FFFFFF;
    background-color: #0085c5;
    border-color: #007cb8;
    display: inline-block;
    font-weight: 400;
    text-align: center;
    vertical-align: middle;
    user-select: none;
    border: 1px solid transparent;
    padding: 0.375rem 0.75rem;
    font-size: 1rem;
    line-height: 1.5;
    border-radius: 0.25rem;
}