写CSS的常用套路(绝对定位实现多重边框)

谁规定按钮只能有一套边框的？利用绝对定位和padding，我们可以给按钮做出3套大小不一的边框来，这样效果更炫了。

HTML:

<button class="btn btn-primary btn-ghost btn-multiple-border-stroke">
  <div class="btn-borders-group">
    <div class="border-top"></div>
    <div class="border-right"></div>
    <div class="border-bottom"></div>
    <div class="border-left"></div>
  </div>
  <div class="btn-borders-group">
    <div class="border-top"></div>
    <div class="border-right"></div>
    <div class="border-bottom"></div>
    <div class="border-left"></div>
  </div>
  <div class="btn-borders-group">
    <div class="border-top"></div>
    <div class="border-right"></div>
    <div class="border-bottom"></div>
    <div class="border-left"></div>
  </div>
  <span class="btn-text">Start</span>
</button>

CSS:

@import url(https://fonts.googleapis.com/css?family=Lato);

body {
  display: flex;
  height: 100vh;
  justify-content: center;
  align-items: center;
  text-align: center;
  background: #1A1E23;
}

.btn {
  --hue: 190;
  --ease-in-duration: 0.25s;
  --ease-out-duration: 0.65s;
  --ease-out-delay: var(--ease-in-duration);
  position: relative;
  padding: 1rem 3rem;
  font-size: 1rem;
  line-height: 1.5;
  color: white;
  text-decoration: none;
  background-color: hsl(var(--hue), 100%, 41%);
  border: 1px solid hsl(var(--hue), 100%, 41%);
  outline: transparent;
  cursor: pointer;
  user-select: none;
  white-space: nowrap;
  transition: 0.25s;

  &:hover {
    background: hsl(var(--hue), 100%, 31%);
  }

  &-primary {
    --hue: 171;
  }

  &-ghost {
    color: hsl(var(--hue), 100%, 41%);
    background-color: transparent;
    border-color: hsl(var(--hue), 100%, 41%);

    &:hover {
      color: white;
    }
  }

  &-multiple-border-stroke {
    border-color: transparent;

    .btn-borders-group {
      position: absolute;
      top: 0;
      left: 0;
      display: flex;
      justify-content: center;
      align-items: center;
      width: 100%;
      height: 100%;
      border: 1px solid hsla(var(--hue), 100%, 41%, 0.35);

      &:nth-child(1) {
        left: -8px;
        padding: 0 8px;
      }

      &:nth-child(2) {
        top: -8px;
        padding: 8px 0;
      }

      &:nth-child(3) {
        top: -4px;
        left: -4px;
        padding: 4px;
      }

      .border-top {
        position: absolute;
        top: 0;
        width: 100%;
        height: 1px;
        background: hsl(var(--hue), 100%, 41%);
        transform: scaleX(0);
        transform-origin: left;
      }

      .border-right {
        position: absolute;
        right: 0;
        width: 1px;
        height: 100%;
        background: hsl(var(--hue), 100%, 41%);
        transform: scaleY(0);
        transform-origin: bottom;
      }

      .border-bottom {
        position: absolute;
        bottom: 0;
        width: 100%;
        height: 1px;
        background: hsl(var(--hue), 100%, 41%);
        transform: scaleX(0);
        transform-origin: left;
      }

      .border-left {
        position: absolute;
        left: 0;
        width: 1px;
        height: 100%;
        background: hsl(var(--hue), 100%, 41%);
        transform: scaleY(0);
        transform-origin: bottom;
      }

      // when unhover, ease-in top, right; ease-out bottom, left

      .border-left {
        transition: var(--ease-out-duration) var(--ease-out-delay) cubic-bezier(0.2, 1, 0.2, 1);
      }

      .border-bottom {
        transition: var(--ease-out-duration) var(--ease-out-delay) cubic-bezier(0.2, 1, 0.2, 1);
      }

      .border-right {
        transition: var(--ease-in-duration) cubic-bezier(1, 0, 0.8, 0);
      }

      .border-top {
        transition: var(--ease-in-duration) cubic-bezier(1, 0, 0.8, 0);
      }
    }

    &:hover {
      color: hsl(var(--hue), 100%, 41%);
      background: transparent;

      .border-top,
      .border-bottom {
        transform: scaleX(1);
      }

      .border-left,
      .border-right {
        transform: scaleY(1);
      }

      // when hover, ease-in bottom, left; ease-out top, right

      .border-left {
        transition: var(--ease-in-duration) cubic-bezier(1, 0, 0.8, 0);
      }

      .border-bottom {
        transition: var(--ease-in-duration) cubic-bezier(1, 0, 0.8, 0);
      }

      .border-right {
        transition: var(--ease-out-duration) var(--ease-out-delay) cubic-bezier(0.2, 1, 0.2, 1);
      }

      .border-top {
        transition: var(--ease-out-duration) var(--ease-out-delay) cubic-bezier(0.2, 1, 0.2, 1);
      }
    }
  }
}