30.纯 CSS 创作一个晃动的公告板

<div class="signboard">
    <div class="sign">THANKS</div>
    <div class="strings"></div>
    <div class="pin top"></div>
    <div class="pin left"></div>
    <div class="pin right"></div>
</div>

html, body {
    margin: 0;
    padding: 0;
    width: 100%;
    height: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
    background: radial-gradient(circle at center 60%,white,saddlebrown)
}
.signboard{
    position: relative;
    width: 400px;
    height: 300px;
    /* border: 1px solid blue; */
}
.sign{
    position: absolute;
    bottom: 0;
    width: 100%;
    height: 200px;
    border-radius: 15px;
    background: burlywood;
    line-height: 200px;
    text-align: center;
    font-family: sans-serif;
    font-weight: bold;
    color: saddlebrown;
    text-shadow: 0 2px 0 rgba(225, 225, 225, 0.3),
                0 -2px 0 rgba(0, 0, 0, 0.7);
}
/* 画出细绳 */
.strings{
    position: absolute;
    width: 150px;
    height: 150px;
    border: 5px solid brown;
    border-right: none;
    border-bottom: none;
    transform: rotate(45deg);
    top: 38px;
    left: 122px;
}
/* 画出细绳顶部的图钉 */
.pin{
    position: absolute;
    width: 25px;
    height: 25px;
    border-radius: 50%;
}
.pin.top{
    background: gray;
    left: 187px;
}
/* 画出木板上左右两侧的图钉 */
.pin.left,
.pin.right{
    background: brown;
    top: 110px;
    box-shadow: 0 2px 0 rgba(255,255,255,0.3);
}
.pin.left{
    left: 80px;
}
.pin.right{
    right: 80px;
}
/* 让signboard晃动起来 */
.signboard{
    animation: swing 1.5s ease-in-out infinite alternate;
    /* 用于指定元素变形的中心点 */
    transform-origin: 200px 13px;
}
@keyframes swing{
    from{
        transform: rotate(10deg);
    }
    to{
        transform: rotate(-10deg);
    }
}