Say I have a simple reveal.js slide like this:
first
If you want to completely remove the space taken by the hidden element after it was shown, you can use the following CSS selector and properties:
.fragment.current-visible.visible:not(.current-fragment) {
display: none;
height:0px;
line-height: 0px;
font-size: 0px;
}
Additionally if you don't want this behavior for other current-visible fragments, you can just add a custom class to your selector and HTML elements.