如何使用纯CSS实现一个转动的自行车车轮的动画效果

效果预览

源代码下载

https://github.com/comehope/front-end-daily-challenges

代码解读

定义 dom，容器中包含 6 个元素：

<div class="wheel">
 <span></span>
 <span></span>
 <span></span>
 <span></span>
 <span></span>
 <span></span>
</div>

居中显示：

body {
 margin: 0;
 height: 100vh;
 display: flex;
 align-items: center;
 justify-content: center;
 background-image: linear-gradient(#555, #222);
}

画出轮圈：

.wheel {
 width: 9em;
 height: 9em;
 font-size: 25px;
 border: 0.4em solid #777;
 border-radius: 50%;
 box-shadow: 0 0 0 0.5em #111;
}

定义辐条的样式：

.wheel {
 display: flex;
 align-items: center;
 justify-content: center;
}

.wheel span {
 position: absolute;
 width: 8em;
 height: 1em;
 border: 0.1em solid;
 border-color: #ccc transparent;
}

定义变量，画出多根幅条：

.wheel span {
 transform: rotate(calc((var(--n) - 1) * 30deg));
}

.wheel span:nth-child(1) {
 --n: 1;
}

.wheel span:nth-child(2) {
 --n: 2;
}

.wheel span:nth-child(3) {
 --n: 3;
}

.wheel span:nth-child(4) {
 --n: 4;
}

.wheel span:nth-child(5) {
 --n: 5;
}

.wheel span:nth-child(6) {
 --n: 6;
}

让车轮转动起来：

.wheel span {
 animation: run 4s linear infinite;
}

@keyframes run {
 to {
 transform: rotate(calc((var(--n) - 1) * 30deg + 360deg));
 }
}

用伪元素画出地面上的线条：

.wheel {
 position: relative;
}

.wheel::before {
 content: '';
 position: absolute;
 width: 15em;
 height: 0.2em;
 top: 11em;
 background-image: linear-gradient(
 to right,
 silver 0, silver 4em,
 transparent 4em, transparent 5em,
 silver 5em, silver 10em,
 transparent 10em, transparent 12em,
 silver 12em, silver 14em,
 transparent 14em, transparent 15em
 );
}

最后，让地面上的线条动起来，形成车轮向前走的效果：

.wheel::before {
 background-position: 15em;
 animation: run2 6s linear infinite;
}
@keyframes run2 {
 to {
 background-position: -15em;
 }
}

大功告成！