【CSS进阶】巧用伪元素before和after制作绚丽效果（中）

<div class="box-line1"></div>

.box-line2,
.box-line2::before,
.box-line2::after {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
}

.box-line2 {
  width: 200px;
  height: 200px;
  margin: auto;
  color: #69ca62;
  box-shadow: inset 0 0 0 1px rgba(105, 202, 98, 0.5);
}

.box-line2::before,
.box-line2::after {
  content: "";
  z-index: 99;
  margin: -5%;
  box-shadow: inset 0 0 0 2px;
  animation: clipMe 8s linear infinite;
}

.box-line2::before {
  animation-delay: -4s;
}

.box-line2:hover::after,
.box-line2:hover::before {
  background-color: rgba(255, 0, 0, 0.3);
}

@keyframes clipMe {

  0%,
  100% {
    clip: rect(0px, 220px, 2px, 0px);
  }

  25% {
    clip: rect(0px, 2px, 220px, 0px);
  }

  50% {
    clip: rect(218px, 220px, 220px, 0px);
  }

  75% {
    clip: rect(0px, 220px, 220px, 218px);
  }
}

@keyframes surround {

  0%,
  100% {
    clip: rect(0px, 220px, 2px, 0px);
  }

  25% {
    clip: rect(0px, 2px, 220px, 0px);
  }

  50% {
    clip: rect(218px, 220px, 220px, 0px);
  }

  75% {
    clip: rect(0px, 220px, 220px, 218px);
  }
}

.box-line1:before,
.box-line1:after {
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
  content: "";
  z-index: 99;
  margin: -5%;
  animation: surround linear infinite 8s;
  box-shadow: inset 0 0 0 2px #69ca62;
}

.box-line1:before {
  animation-delay: -4s;
}

.box-line1 {
  border: 1px solid #69ca62;
  position: absolute;
  left: 500px;
  top: 200px;
  margin: auto;
  width: 200px;
  height: 200px;
  margin: auto;
}

<div class="tip" data-tip="CSS伪类">CSS伪类</div>

.tip::after {
  content: attr(data-tip);
  display: none;
  position: absolute;
  padding: 5px 10px;
  left: 15%;
  bottom: 100%;
  width: 150px;
  margin-bottom: 12px;
  transform: translateX(-50%);
  font-size: 12px;
  background: #000;
  color: #fff;
  cursor: default;
  border-radius: 4px;
}

.tip::before {
  content: " ";
  position: absolute;
  display: none;
  left: 15%;
  bottom: 100%;
  transform: translateX(-50%);
  margin-bottom: 3px;
  width: 0;
  height: 0;
  border-left: 6px solid transparent;
  border-right: 6px solid transparent;
  border-top: 9px solid #000;
}

.tip:hover::after,
.tip:hover::before {
  display: block;
}

<div class="box effect2">
  <h3>CSS 伪类盒子阴影</h3>
</div>

.effect2 {
    position: relative;
}

.effect2::before, .effect2::after {
    z-index: -1;
    position: absolute;
    content: "";
    bottom: 15px;
    left: 10px;
    width: 50%;
    top: 80%;
    max-width: 300px;
    background: #777;
    -webkit-box-shadow: 0 15px 10px #777;
    -moz-box-shadow: 0 15px 10px #777;
    box-shadow: 0 15px 10px #777;
    -webkit-transform: rotate(-3deg);
    -moz-transform: rotate(-3deg);
    -o-transform: rotate(-3deg);
    -ms-transform: rotate(-3deg);
    transform: rotate(-3deg);
}
.effect2::after {
    -webkit-transform: rotate(3deg);
    -moz-transform: rotate(3deg);
    -o-transform: rotate(3deg);
    -ms-transform: rotate(3deg);
    transform: rotate(3deg);
    right: 10px;
    left: auto;
}

    <div class="sm-box flex">
        <div class="menu-tabs active">首页</div>
        <div class="menu-tabs">新闻</div>
        <div class="menu-tabs">视频</div>
        <div class="menu-tabs">图片</div>
    </div>

.menu-tabs {
  display: block;
  padding: 0.25rem 1.5rem;
  clear: both;
  font-weight: 400;
  color: #212529;
  text-align: inherit;
  white-space: nowrap;
  background-color: transparent;
  width: 50px;
  border: 0;
  height: 35px;
  justify-content: center;
  display: flex;
  cursor: pointer;
}

.menu-tabs:hover {
  color: #20a884;
  position: relative;
}

.menu-tabs:hover:after {
  position: absolute;
  content: "";
  border: 1px solid #20a884;
  width: 3rem;
  left: 0;
  bottom: 0;
  margin-left: 50%;
  transform: translateX(-50%);
}

.active {
  position: relative;
  color: #20a884;
}

.flex {
  display: flex;
}

.active::after {
  position: absolute;
  content: "";
  border: 1px solid #20a884;
  width: 3rem;
  left: 0;
  bottom: 0;
  margin-left: 50%;
  transform: translateX(-50%);
}

<div class="container">
   <div class="overlay">
      <h1>A blurred overlay</h1>
     <p>... mask or whatever
     <br>that is responsive and could be cross-browser compatible back to IE9</p>
   </div>
</div>

.container {
  width: 100%;
  height: 100%;
  margin: 0;
}

.container,
.overlay:before {
  background: url(https://wow.techbrood.com/assets/landing.jpg) no-repeat fixed 0 0 / cover;
}

.container {
  -webkit-box-align: center;
  -webkit-align-items: center;
  -ms-flex-align: center;
  align-items: center;
  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-pack: center;
  -webkit-justify-content: center;
  -ms-flex-pack: center;
  justify-content: center;
}

.overlay {
  max-height: 200px;
  margin: 0 auto;
  max-width: 768px;
  padding: 50px;
  position: relative;
  color: white;
  font-family: "Lato";
  position: relative;
  text-align: center;
  z-index: 0;
}

.overlay:before {
  content: "";
  -webkit-filter: blur(100px);
  filter: blur(100px);
  height: 100%;
  left: 0;
  position: absolute;
  top: 0;
  width: 100%;
  z-index: -1;
}

<span class="lanhu_text">
   本站由叫我詹躲躲提供技术支持
</span>

.lanhu_text {
  position: relative;
  color: #2878ff;
}

.lanhu_text::before {
  content: "";
  width: 80px;
  height: 20px;
  position: absolute;
  left: -86px;
  top: 0;
  background: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAFAAAAABCAYAAABJwyn/AAAAjElEQVQoU22NSw7CQAxDX8ahICF2HIDTcf9d1c8kaDpthQSL6CmxHRuk8cZfMxqf6DGh+Y5uCxquaB7xdUCXilZHWvBorEiOaqAKrkRRUEmUOw283TKRRb9b4GnIEpWmGYrA237kDh1w6J5N7zzzZv13gtuvT7t++jefUTYmwvpk7v3fPaCzn//9LfsBvRpHnliu+xMAAAAASUVORK5CYII=) 0 no-repeat;
}

.lanhu_text::after {
  content: "";
  width: 80px;
  height: 20px;
  position: absolute;
  right: -86px;
  top: 0;
  background: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAFAAAAABCAYAAABJwyn/AAAAhElEQVQoU22OSw7CQAxDXzJDWbHiEFyRJQflFggJSjyDph9oC6snx45lO52rrKJqzIyNlkFUPv6vnv+3uW9vrPpBq77/uWFPAXnrnfYVQ16JiWq0stjvxKB9vDc/MeaXWo5cqDEFUkKpEuEoB3ollHvUZ9QV4rFD3R3d9ujwJK5HxAW9AStemAIOwCNlAAAAAElFTkSuQmCC) 100% no-repeat;
}