.radio() {
    box-sizing: border-box;
}
.circle(@r) {
    width: @r;
    height: @r;
    display: inline-block;
    border-radius: 50%;
}
.center() {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate3d(-50%, -50%, 0);
}