label.a.slide {
    animation-duration: 1s;
    animation-name: slideinfromleft;
    position: relative;
}

@keyframes slideinfromleft {
    from {
        left: -640px;
    }

    to {
        left: 0;
    }
}

label.b.slide {
    animation-duration: 1s;
    animation-name: slideinfromright;
    position: relative;
}

@keyframes slideinfromright {
    from {
        left: 640px;
    }

    to {
        left: 0;
    }
}