CSS3滑动渐变动画-工作原理

Question

Following code produces sliding gradient animation without any line of javascript code:

 html { height: 100% } body { height: 100%; margin: 0 } @keyframes loading { from { background-position: -5000% 0, 0 0 } to { background-position: 5000% 0, 0 0 } } .skeleton { height: 100%; animation-name: loading; animation-duration: 1.5s; animation-iteration-count: infinite; background-color: #fff; background-repeat: no-repeat; background-image: linear-gradient(90deg, hsla(0, 0%, 100%, 0), hsla(0, 0%, 100%, .8) 50%, hsla(0, 0%, 100%, 0)), linear-gradient(#e5e5e5 100%, transparent 0); background-size: 99% 100%; } 

 <div class="skeleton"></div> 

I experimented with some properties and still do not understand how it works. Especially, when background-size: 99% 100%; is changed to background-size: 100% 100%; animation slides in opposite direction!

Could you explain it?

Answer 1

I don't know what's your browser and its version. But on my computer, if background-size: 100% 100% then the animation will be stop. (Actually, the background-position will be ignored)

The idea of this trick is moving background-image (linear-gradient) by background-position . (Check the comment in code below for detail)

About your second question, you should refer this answer CSS background-position ignored when using background-size . A quick summary, you can't use percent for background-position if background-size reaches to 100%. This happens because the image in background has no space to move.

If you insist to use background-size with 100%. I afraid you have to use absolute values.

BTW, I've upgraded the code. Now it looks better.

 html { height: 100% } body { height: 100%; margin: 0 } @keyframes loading {/* original code */ from {/* This is the position of image of the first frame */ background-position: -5000% 0, 0 0 } to {/* This is the pos of img of the last frame */ background-position: 5000% 0, 0 0 } } @keyframes betterLoading { 0% {/* This is the position of image of the first frame */ background-position: -5000% 0, 0 0 } 50% { /* This is the pos of img of a frame in the middle happening animation */ /* If duration is 1s then the pos below will be at 0.5s */ background-position: 5000% 0, 0 0 } 100% {/* This is the pos of img of the last frame */ background-position: -5000% 0, 0 0 } } .skeleton { height: 100%; animation-name: betterLoading; animation-duration: 1.5s; animation-iteration-count: infinite; background-color: #fff; background-repeat: no-repeat; background-image: linear-gradient(90deg, hsla(0, 0%, 100%, 0), hsla(0, 0%, 100%, .8) 50%, hsla(0, 0%, 100%, 0)), linear-gradient(green 100%, transparent 0); background-size: 99% 100%, cover; } 

 <div class="skeleton"></div>