57.1拓展之纯 CSS 创作黑暗中的眼睛和嘴巴

效果地址：https://scrimba.com/c/cJ8NPpU2

HTML code：

<div class="eyes">
    <span class="left"></span>
    <span class="right"></span>
</div>

CSS code：

html, body {
    margin: 0;
    padding: 0;
}
/* 设置body的子元素水平垂直居中 */
body{
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: black;
}
/* 设置容器尺寸 */
.eyes{
    position: relative;
    width: 30em;
    height: 10em;
    /* border: 1px solid white; */
    font-size: 12px;
}
.eyes > * {
    /* 设置宽高包含内边距/边框和内容 */
    box-sizing: border-box;
    position: absolute;
    width: 10em;
    height: 10em;
    border: solid white;
    /* 画眼球 */
    border-width: 0 3em;
    animation: blink 2s linear infinite;
}
.eyes .left{
    left: 0;
    border-radius: 50%;
    /* 使双眼旋转90度变为正常的眼睛 */
    transform: rotate(90deg);
}
.eyes .right {
    right : 0;
    border-radius: 50%;
    transform: rotate(90deg);
}
/* 定义眨眼的动画 */
@keyframes blink{
    40%, 60%{
        border-width: 0 3em;
    }
    50% {
        border-width: 0 5em;
    }
}
/* 用.eyes的伪元素::after画出嘴巴 */
.eyes::after{
    position: absolute;
    top: 10em;
    left: 5em;
    content:'';
    width: 20em;
    height: 10em;
    border-bottom: solid white;
    border-width: 3em 0;
    border-radius: 50%;
}