footer {
    font-size: smaller;
    text-align: center;
    position: absolute;
    width: 100%;
    height: 32px; /* Line-height 19px + margin-top 24px + margin-bottom 8px */
    bottom: 0;
    color: #aaa;
}

@media screen and (max-height: 439px) { /* 407px (sign in form height) + 32px (footer height) */
    footer {
        display: none;
    }
}