mdb-ui-kit/scss/_dividers.scss

hr {
  &.on-dark {
    color: lighten($black, 10%);
  }

  &.on-light {
    color: lighten($white, 10%);
  }

  @media (-webkit-min-device-pixel-ratio: 0.75),
  (min--moz-device-pixel-ratio: 0.75),
  (-o-device-pixel-ratio: 3/4),
  (min-device-pixel-ratio: 0.75),
  (min-resolution: 0.75dppx),
  (min-resolution: 120dpi) {
    height: 0.75px;
  }

  @media (-webkit-min-device-pixel-ratio: 1),
  (min--moz-device-pixel-ratio: 1),
  (-o-device-pixel-ratio: 1),
  (min-device-pixel-ratio: 1),
  (min-resolution: 1dppx),
  (min-resolution: 160dpi) {
    height: 1px;
  }
  @media (-webkit-min-device-pixel-ratio: 1.33),
  (min--moz-device-pixel-ratio: 1.33),
  (-o-device-pixel-ratio: 133/100),
  (min-device-pixel-ratio: 1.33),
  (min-resolution: 1.33dppx),
  (min-resolution: 213dpi) {
    height: 1.333px;
  }
  @media (-webkit-min-device-pixel-ratio: 1.5),
  (min--moz-device-pixel-ratio: 1.5),
  (-o-device-pixel-ratio: 3/2),
  (min-device-pixel-ratio: 1.5),
  (min-resolution: 1.5dppx),
  (min-resolution: 240dpi) {
    height: 1.5px;
  }

  @media (-webkit-min-device-pixel-ratio: 2),
  (min--moz-device-pixel-ratio: 2),
  (-o-device-pixel-ratio: 2/1),
  (min-device-pixel-ratio: 2),
  (min-resolution: 2dppx),
  (min-resolution: 380dpi) {
    height: 2px;
  }

  @media (-webkit-min-device-pixel-ratio: 3),
  (min--moz-device-pixel-ratio: 3),
  (-o-device-pixel-ratio: 3/1),
  (min-device-pixel-ratio: 3),
  (min-resolution: 3dppx),
  (min-resolution: 480dpi) {
    height: 3px;
  }

  @media (-webkit-min-device-pixel-ratio: 4),
  (min--moz-device-pixel-ratio: 4),
  (-o-device-pixel-ratio: 4/1),
  (min-device-pixel-ratio: 3),
  (min-resolution: 4dppx),
  (min-resolution: 640dpi) {
    height: 4px;
  }

}