Fix scrolling performance with CSS will-change property (background-attachment: css)

gistfile1.txt

.fixed-background-container
  background: transparent
  color: $white

  &:before
    content: ''
    position: fixed
    height: 100%
    width: 100%
    top: 0
    left: 0
    background-color: white
    background: url("/path/to/img") no-repeat center center
    background-size: cover
    will-change: tranform
    z-index: -1