Css3基于 box-shadow的鼠标悬停

<div class="buttons">  <h1>简单的悬停效果基于 <code>box-shadow</code></h1>  <button class="fill">Fill In</button>  <button class="pulse">Pulse</button>  <button class="close">Close</button>  <button class="raise">Raise</button>  <button class="up">Fill Up</button>  <button class="slide">Slide</button>  <button class="offset">Offset</button></div>

<style>    .fill:hover,    .fill:focus {      box-shadow: inset 0 0 0 2em var(--hover);    }    .pulse:hover,    .pulse:focus {      -webkit-animation: pulse 1s;              animation: pulse 1s;      box-shadow: 0 0 0 2em rgba(255, 255, 255, 0);    }    @-webkit-keyframes pulse {      0% {        box-shadow: 0 0 0 0 var(--hover);      }    }    @keyframes pulse {      0% {        box-shadow: 0 0 0 0 var(--hover);      }    }    .close:hover,    .close:focus {      box-shadow: inset -3.5em 0 0 0 var(--hover), inset 3.5em 0 0 0 var(--hover);    }    .raise:hover,    .raise:focus {      box-shadow: 0 0.5em 0.5em -0.4em var(--hover);      -webkit-transform: translateY(-0.25em);              transform: translateY(-0.25em);    }    .up:hover,    .up:focus {      box-shadow: inset 0 -3.25em 0 0 var(--hover);    }    .slide:hover,    .slide:focus {      box-shadow: inset 6.5em 0 0 0 var(--hover);    }    .offset {      box-shadow: 0.3em 0.3em 0 0 var(--color), inset 0.3em 0.3em 0 0 var(--color);    }    .offset:hover, .offset:focus {      box-shadow: 0 0 0 0 var(--hover), inset 6em 3.5em 0 0 var(--hover);    }    .fill {      --color: #a972cb;      --hover: #cb72aa;    }    .pulse {      --color: #ef6eae;      --hover: #ef8f6e;    }    .close {      --color: #ff7f82;      --hover: #ffdc7f;    }    .raise {      --color: #ffa260;      --hover: #e5ff60;    }    .up {      --color: #e4cb58;      --hover: #94e458;    }    .slide {      --color: #8fc866;      --hover: #66c887;    }    .offset {      --color: #19bc8b;      --hover: #1973bc;    }    button {      color: var(--color);      -webkit-transition: 0.25s;      transition: 0.25s;    }    button:hover, button:focus {      border-color: var(--hover);      color: #fff;    }    body {      color: #fff;      background: #17181c;      font: 300 1em 'Fira Sans', sans-serif;      -webkit-box-pack: center;      -ms-flex-pack: center;      justify-content: center;      -ms-flex-line-pack: center;      align-content: center;      -webkit-box-align: center;      -ms-flex-align: center;      align-items: center;      text-align: center;      min-height: 100vh;      display: -webkit-box;      display: -ms-flexbox;      display: flex;    }    button {      background: none;      border: 2px solid;      font: inherit;      line-height: 1;      margin: 0.5em;      padding: 1em 2em;    }    h1 {      font-weight: 400;    }    code {      color: #e4cb58;      font: inherit;    }</style>