SOURCE

<div class="container">
  上边是斜的
</div>

// 根据传递的角度计算斜坡高度
@function get-tilted-height($angle) {
  $a: (100% / 1%);
  $A: (90deg - $angle);
  $c: ($a / sin($A));
  $b: sqrt(pow($c, 2) - pow($a, 2));

  @return (abs($b) * 1%);
}

// 编写 mixin
@mixin tilted($angle, $color, $position: 'top', $pseudo: 'before') {
  $height: get-tilted-height($angle);

  position: relative;
  background-color: $color;

  &::#{$pseudo} {
    content: '';
    padding-top: $height;
    position: absolute;
    left: 0;
    right: 0;

    @if ($position == 'top') {
      bottom: 100%;
      background-image: linear-gradient($angle, $color 50%, transparent 50%);
    } @else {
      top: 100%;
      background-image: linear-gradient($angle, transparent 50%, $color 50%);
    }
  }
}

/*
 * Demo styles
 */

*, ::before, ::after {
  box-sizing: inherit;
}

body {
  background-color: rgb(223, 231, 238);
}

.container {
  @include tilted(3deg, rgb(255, 255, 255));
  padding: 0 1em;
  width:80%;
  margin: 100px auto;
  filter: drop-shadow(0 1em 1em rgba(0, 0, 0, 0.1));
}