Moving Things Around With CSS Transitions

Moving Things Around With CSS Transitions

As I indicated in my last blog post, my new blog theme has a “pop up” Dan in the upper-left corner. Assuming that you’re not using Internet Explorer, then when you move your mouse cursor over it, my head will “duck” back behind the bar below it.

My head "pops up" in the top-left hand corner of the site, and hides when you hover your mouse cursor over it.

My head "pops up" in the top-left hand corner of the site, and hides when you hover your mouse cursor over it.

This is all done without any Javascript whatsoever: it’s pure CSS. Here’s how it’s done:

<div class="sixteen columns">
  <div id="dans-creepy-head"></div>
  <h1 id="site-title" class="graphic">
    <a href="http://www.scatmania.org/" title="Scatmania">Scatmania</a>
  </h1>
  <span class="site-desc graphic">
    The adventures and thoughts of &quot;Scatman&quot; Dan Q
  </span>
</div>

The HTML for the header itself is pretty simple: there’s a container (the big blue bar) which contains, among other things, a <div> with the id "dans-creepy-head". That’s what we’ll be working with. Here’s the main CSS:

#dans-creepy-head {
  position: absolute;
  top: -24px;
  left: 15px;
  width: 123px;
  height: 133px;
  background: url(/dans-creepy-head.png) top left no-repeat;
  transition: all 800ms;
  -o-transition: all 800ms;
  -webkit-transition: all 800ms;
  -moz-transition: all 800ms;
}
#dans-creepy-head:hover {
  top: 100px;
  height: 60px;
}

The CSS sets a size, position, and background image to the <div>, in what is probably a familiar way. A :hover selector changes the style to increase the distance from the top of the container (from -24px to 100px) and to decrease the height, cropping the image (from 133px to 60px – this was necessary in this case to prevent the bottom of the image from escaping out from underneath the masking bar that it’s supposed to be “hiding behind”). With just that code, you’d have a perfectly workable “duck”, but with a jerky, one-step animation.

The transition directive (and browser-specific prefix versions -o-transition, -webkit-transition, and -moz-transition, for compatability) are what makes the magic happen. This element specifies that any ("all") style is changed on this element (whether via CSS directives, as in this case, or by a change of class or properties by a Javascript function), that a transition effect will be applied to those changes. My use of  "all" is a lazy catch-all – I could have specified the individual properties ( top and  height) that I was interested in changing, and even put different periods on each, but I’ll leave it to you to learn about CSS3 transition options for yourself. The  800ms is the duration of the transition: in my case, 0.8 seconds.

html.ie #dans-creepy-head:hover {
  top: -24px;
  height: 133px;
}
@media (max-width: 780px) {
  #dans-creepy-head {
    display: none;
  }
}

I apply some CSS to prevent the :hover effect from taking place in Internet Explorer, which doesn’t support transitions. The "ie" class is applied to the  <html> tag using Paul Irish’s technique, so it’s easy to detect and handle IE users without loading separate stylesheet files for them. And finally, in order to fit with my newly-responsive design, I make the pop-up head disappear when the window is under 780px wide (at which point there’d be a risk of it colliding with the title).

That’s all there is to it! A few lines of CSS, and you’ve got an animation that degrades gracefully. You could equally-well apply transformations to links (how about making them fade in or out, or change the position of their background image?) or, with a little Javascript, to your tabstrips and drop-down menus.

Dan Q is a software engineer, a director of a voluntary organisation, a trainee counsellor, a keen geocacher, and an amateur magician. He lives with his partner and her husband in a polyamorous triad, and occasionally finds time to blog.