CSS3 Gradient flickers on hover

Question

I'm playing around with a CSS3 Gradient and trying to move it in on mouseover. As you can see from this jsFiddle, the CSS gradient appears on :hover; however, it seems to flickers a few times.

FYI, so far, this has been tested on Chrome v30 / Firefox v24 / Safari v5.1.

Separately, both have turned out to be working solutions, but combined, I get the flickering effect.

nav li {
    width: 90px;
    padding-right: 15px;
    padding-left: 15px;
    height: 30px;
    border: 1px solid #000;
    float: left;
    list-style-type: none;

    background-position: -200px -200px;
    -webkit-transition: background 1s ease-out;
    -moz-transition: background 1s ease-out;
    -o-transition: background 1s ease-out;
    transition: background 1s ease-out;
}

nav li:hover {
    background-position: 200px 0;
    background: url(data:image/svg+xml;base64,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);
    background: -moz-linear-gradient(top,  rgba(255,255,255,0.2) 0%, rgba(96,96,96,0.2) 100%);
    background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,rgba(255,255,255,0.2)), color-stop(100%,rgba(96,96,96,0.2)));
    background: -webkit-linear-gradient(top,  rgba(255,255,255,0.2) 0%,rgba(96,96,96,0.2) 100%);
    background: -o-linear-gradient(top,  rgba(255,255,255,0.2) 0%,rgba(96,96,96,0.2) 100%);
    background: -ms-linear-gradient(top,  rgba(255,255,255,0.2) 0%,rgba(96,96,96,0.2) 100%);
    background: linear-gradient(to bottom,  rgba(255,255,255,0.2) 0%,rgba(96,96,96,0.2) 100%);
    filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#33ffffff', endColorstr='#33606060',GradientType=0 );
}

I've tried limiting the animation using animation-iteration-count, but as I've figured out, this only seems to work with animations and @keyframes. I've also read on a few different sites that @keyframes don't yet support CSS Gradient animation.

Answer 1

The flickering effect is due to the difference between your element height (30px) and the offsets you've given for the background (-200px -> 0px).

Basically, it's scrolling past the view six times in the one second transition (because 30 goes into 200 six times), which is what is giving you the flickering effect. You can see the effect more easily if you increase the transition time a bit, say to 5 seconds; this will make it more obvious what it happening. (obviously you can set it back when you're done testing)

If you change the inital background-position to -30px instead of -200px, you'll get it scrolling into view just one time, and thus no flicker.

Hope that helps.