A mixin to implement the 'Bank Note' pattern from https://www.heropatterns.com/

wave-mixin.scss

@mixin wave($base-color: #235937, $opacity: 0.4) {
  $alt: darken($base-color, 5%);
  background-color: $base-color;
  background-image: url("data:image/svg+xml,%3Csvg width='100' height='20' viewBox='0 0 100 20' xmlns='http://www.w3.org/2000/svg'%3E%3Cpath d='M21.184 20c.357-.13.72-.264 1.088-.402l1.768-.661C33.64 15.347 39.647 14 50 14c10.271 0 15.362 1.222 24.629 4.928.955.383 1.869.74 2.75 1.072h6.225c-2.51-.73-5.139-1.691-8.233-2.928C65.888 13.278 60.562 12 50 12c-10.626 0-16.855 1.397-26.66 5.063l-1.767.662c-2.475.923-4.66 1.674-6.724 2.275h6.335zm0-20C13.258 2.892 8.077 4 0 4V2c5.744 0 9.951-.574 14.85-2h6.334zM77.38 0C85.239 2.966 90.502 4 100 4V2c-6.842 0-11.386-.542-16.396-2h-6.225zM0 14c8.44 0 13.718-1.21 22.272-4.402l1.768-.661C33.64 5.347 39.647 4 50 4c10.271 0 15.362 1.222 24.629 4.928C84.112 12.722 89.438 14 100 14v-2c-10.271 0-15.362-1.222-24.629-4.928C65.888 3.278 60.562 2 50 2 39.374 2 33.145 3.397 23.34 7.063l-1.767.662C13.223 10.84 8.163 12 0 12v2z' fill='#{$alt}' fill-opacity='#{$opacity}' fill-rule='evenodd'/%3E%3C/svg%3E");
}

/* 
Example usage 
- For a new variation, pass custom parameters
*/
.bg-wave {
  $color: #222222;
  $opacity: 0.9;
  @include wave($color, $opacity);
  color: white;
}