I'm not sure if this was how CSSTricks did it, but I assume that the slide function is either js or a -webkit-transition. Using the transition function in combo with a position change upon clicking the bar could yield that effect. I'm no js expert, but code like:
It looks like just a simple jquery accordion effect, and disabling js shows that it is done via scripting. Without it, the content is all extended (nice bit o' progressive enhancement there).
function HideContent(d) {
document.getElementById(d).style.display = "none";
}
function ShowContent(d) {
document.getElementById(d).style.display = "block";
}
function ReverseDisplay(d) {
if(document.getElementById(d).style.display == "block") { document.getElementById(d).style.display = "none"; }
else { document.getElementById(d).style.display = "block"; }
}
would show the divs containing the links. Again, not an expert, just thinking out loud.
Google brings up a number of good tutorials on creating the effect. Hope that helps.