效果预览
按下右侧的“点击预览”按钮在当前页面预览，点击链接全屏预览。
https://codepen.io/zhang-ou/pen/deNqdV
可交互视频教程
此视频是可以交互的，你可以随时暂停视频，编辑视频中的代码。
请用 chrome, safari, edge 打开观看。
https://scrimba.com/c/cvrwJAK
源代码下载
请从 github 下载。
https://github.com/comehope/front-end-daily-challenges/tree/master/008-charging-loader-animation
代码解读
定义 dom，只有一个容器元素：
<div class="battery"></div>居中显示：
html, body {height: 100%;display: flex;align-items: center;justify-content: center;background: linear-gradient(to bottom, teal, aqua);
}画出电池的主体轮廓：
.battery {width: 6em;height: 3em;color: midnightblue;border: 0.5em solid currentColor;border-radius: 0.2em;font-size: 2em;
}画出电池的突起：
.battery {position: relative;
}.battery::after {content: '';position: absolute;width: 0.5em;height: 2em;background-color: currentColor;top: 0.5em;right: -1em;border-radius: 0 0.2em 0.2em 0;
}画出充电电量：
.battery {background-image: linear-gradient(to right, whitesmoke, whitesmoke);background-repeat: no-repeat;background-size: 30% 80%;background-position: 0.3em 50%;
}定义和应用动画效果：
@keyframes charge {from {background-size: 10% 80%;}to {background-size: 95% 80%;}
}.battery {animation: charge 5s linear infinite;
}最后，把动画的时间函数由线性变化改为步长变化：
.battery {animation: charge 5s steps(8) infinite;
}大功告成！
知识点
linear-gradient() https://developer.mozilla.org/en-US/docs/Web/CSS/linear-gradient
background-size https://developer.mozilla.org/en-US/docs/Web/CSS/background-size
background-position https://developer.mozilla.org/en-US/docs/Web/CSS/background-position
steps() https://developer.mozilla.org/en-US/docs/Web/CSS/single-transition-timing-function#Timing_functions
currentColor https://developer.mozilla.org/en-US/docs/Web/CSS/color_value#Values
border-radius https://developer.mozilla.org/en-US/docs/Web/CSS/border-radius