CSS3 equivalent to jQuery slideUp and slideDown?

You could do something like this:

#youritem .fade.in {
    animation-name: fadeIn;
}

#youritem .fade.out {
    animation-name: fadeOut;
}

@keyframes fadeIn {
    0% {
        opacity: 0;
        transform: translateY(startYposition);
    } 
    100% {
        opacity: 1;
        transform: translateY(endYposition);
    }
}

@keyframes fadeOut {
    0% {
        opacity: 1;
        transform: translateY(startYposition);
    } 
    100% {
        opacity: 0;
        transform: translateY(endYposition);
    }
}

Example – Slide and Fade:

This slides and animates the opacity – not based on height of the container, but on the top/coordinate.
View example

Example – Auto-height/No Javascript: Here is a live sample, not needing height – dealing with automatic height and no javascript.
View example