9.纯 CSS 创作一种按钮被瞄准的交互特效

原文地址：https://segmentfault.com/a/1190000014680999

吃鸡倍镜，哈哈哈

HTML代码：

<div class="box">
       <span>BUTTON</span>
       <span class="left"></span>
       <span class="right"></span>
       <span class="top"></span>
       <span class="bottom"></span>
</div>

CSS代码：

html, body {
    margin: 0;
    padding: 0;
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
    color: black;
}
.box{
    width:9em;
    height:3em;
    text-align: center;
    line-height: 3em;
    font-size: 30px;
    /* 字母间距 */
    letter-spacing: 0.2em;
    position: relative;
    filter: blur(2px);
    transition: 1s;
}
.box:hover {
    filter: blur(0.2px);
}
.box::after {
    content: '';
    position: absolute;
    width: 3em;
    height: 3em;
    border: 1px solid red;
    border-radius: 50%;
    left: 3em;
    filter: opacity(0);
}
.box span:not(:first-child) {
    position: absolute;
    background-color: red;
    filter: opacity(0);
}

.box:hover::after,
.box:hover span:not(:first-child) {
    animation: aim 1s linear infinite alternate;
}

.box span.top,
.box span.bottom {
    width: 1px;
    height: 3em;
    left: 50%;
}
.box span.top {
    top: -3em;
}
.box span.bottom {
    bottom: -3em;
}
.box span.left,
.box span.right {
    width: 3em;
    height: 1px;
    top: 50%;
}
.box span.left {
    left: 0;
}
.box span.right {
    right: 0;
}
@keyframes aim {
    from {
        filter: opacity(0.2);
    }
    to {
        filter: opacity(0.8);
    }
}