css3 animation 实现书页加载icon

使用css动画实现类似微信读书加载图标的效果，效果图如下：

实现过程

• 页面DOM，定义一个 book-icon 容器，里面有 page-left、page-right 两个书页，书页内各有 3 个 <span>表示行。

<div class="book-icon">
    <div class="page-left">
        <span></span>
        <span></span>
        <span></span>
    </div>
    <div class="page-right">
        <span></span>
        <span></span>
        <span></span>
    </div>
</div>

• book-icon 、page 、span 的样式

.book-icon {
    width: 15em;
    height: 9em;
    border: 0.4em solid #ddd;
    border-radius: 0.8em;
    display: flex;
    background-color: #f5f5f5;
}

.icon-left,
.icon-right {
    width: 50%;
    padding: 1.2em;
    display: flex;
    flex-direction: column;
    justify-content: space-around;
}

.icon-right {
    border-left: 0.4em solid #ddd;
}

.icon-right >span,
.icon-left >span {
    border-top: 0.4em solid #ddd;
    width: 0;
    animation: 3s linear infinite;
}

• span 的动画，每一行逐渐展开

@keyframes row_1 {
    0% {
        width: 0;
    }
    16.67%, 100% {
        width: 100%;
    }
}
@keyframes row_2 {
    16.67% {
        width: 0;
    }
    33.33%, 100% {
        width: 100%;
    }
}
@keyframes row_3 {
    33.33% {
        width: 0;
    }
    50%, 100% {
        width: 100%;
    }
}
@keyframes row_4 {
    50% {
        width: 0;
    }
    66.67%, 100% {
        width: 100%;
    }
}
@keyframes row_5 {
    66.67% {
        width: 0;
    }
    83.33%, 100% {
        width: 100%;
    }
}
@keyframes row_6 {
    83.33% {
        width: 0;
    }
    100% {
        width: 100%;
    }
}

• 添加动画到 span 上

.page-left >span:nth-child(1) {
    animation-name: row_1;
}

.page-left >span:nth-child(2) {
    animation-name: row_2;
}

.page-left >span:nth-child(3) {
    animation-name: row_3;
}

.page-right >span:nth-child(1) {
    animation-name: row_4;
}

.page-right >span:nth-child(2) {
    animation-name: row_5;
}

.page-right >span:nth-child(3) {
    animation-name: row_6;
}

到此，一个简单的书页加载动画已实现，是否有更加简洁的方案还有待思考。