23.1纯 CSS 创作一个菜单反色填充特效

<nav>
    <ul>
        <li><span>Home</span></li>
    </ul>
</nav>

html, body {
    margin: 0;
    padding: 0;
    width: 100%;
    height: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
    background: linear-gradient(to right bottom,gold, chocolate);
}
/* 为容器设置宽高，此处定义的变量 x 和 y 后面还会用到 */
:root{
    --x: 5em;
    --y: 1.5em;
}
nav ul{
    padding: 0;
}
nav ul li{
    position: relative;
    width: var(--x);
    height: var(--y);
    margin: 0.5em;
    line-height: var(--y);
    list-style-type: none;
    font-size: 40px;
    text-align: center;
    font-family: sans-serif;
    background-color: white;
    border: 2px solid black;
    letter-spacing: 0.1em;
    /* overflow: hidden; */
}
/* 用伪元素画出一个小球，放到菜单项左端 */
nav ul li::before{
    position: absolute;
    content: ‘‘;
    width: 0;
    height: var(--y);
    background-color: black;
    top: 0;
    left: 0;
    transition: 0.5s ease-out;
}
/* 用 mix-blend-mode 设置色彩混合模式，使小球覆盖的文字反色显示 */
nav ul li span{
    color: white;
    mix-blend-mode: difference;
}
nav ul li:hover::before{
    width: var(--x);
}