mdb-ui-kit/scss/_checkboxes.scss

// http://www.google.com/design/spec/components/selection-controls.html#selection-controls-checkbox
.checkbox label,
label.checkbox-inline {
  padding-left: 0; // Reset for Bootstrap rule
  cursor: pointer;

  .checkbox-decorator {
    position: relative;
    top: 3px;
    vertical-align: middle;
    &::before { // FIXME: document why this is necessary (doesn't seem to be on chrome)
      position: absolute;
      left: 0;
      z-index: 1;
      display: block;
      width: $bmd-checkbox-size;
      height: $bmd-checkbox-size;
      margin: 0;
      content: "";
      background-color: rgba($black, .84);
      border-radius: 100%;
      opacity: 0;
      transform: scale3d(2.3, 2.3, 1);
    }

    .check {
      position: relative;
      z-index: 1;
      display: inline-block;
      width: $bmd-checkbox-size;
      height: $bmd-checkbox-size;
      overflow: hidden;
      border: $bmd-checkbox-border-size solid $bmd-checkbox-border-color;
      border-radius: $border-radius;

      // checkbox outline
      &::before {
        position: absolute;
        display: block;
        width: 0;
        height: 0;
        margin-top: -4px;
        margin-left: 6px;
        content: "";
        box-shadow: 0 0 0 0,
        0 0 0 0,
        0 0 0 0,
        0 0 0 0,
        0 0 0 0,
        0 0 0 0,
        0 0 0 0 inset;
        transform: rotate(45deg);
        animation: checkbox-off;

        .is-focused & {
          // Prevent checkbox animation and ripple effect on page load
          animation: checkbox-off $bmd-checkbox-animation-check forwards;
        }
      }
    }
  }

  input[type=checkbox] {

    // Hide native checkbox
    position: absolute;
    left: 0;
    z-index: -1;
    width: 0;
    height: 0;
    margin: 0;
    overflow: hidden;
    pointer-events: none;
    opacity: 0;

    &:focus + .checkbox-decorator .check::after {
      opacity: 0.2;
    }

    &:checked {

      // FIXME: once working - combine further to reduce code
      + .checkbox-decorator .check {
        color: $bmd-checkbox-checked-color;
        border-color: $bmd-checkbox-checked-color;
      }

      + .checkbox-decorator .check::before {
        color: $bmd-checkbox-checked-color;
        box-shadow: 0 0 0 10px,
        10px -10px 0 10px,
        32px 0 0 20px,
        032px 0 20px,
        -5px 5px 0 10px,
        20px -12px 0 11px;
        animation: checkbox-on $bmd-checkbox-animation-check forwards;
      }

      + .checkbox-decorator::before {
        animation: rippleOn;
        .is-focused & {
          // Prevent checkbox animation and ripple effect on page load
          animation: rippleOn $bmd-checkbox-animation-ripple;
        }
      }

      + .checkbox-decorator .check::after {
        //background-color: $brand-success; // FIXME: seems like tho wrong color, test and make sure it can be removed
        animation: rippleOn $bmd-checkbox-animation-ripple forwards; // Ripple effect on check
      }
    }

    &:not(:checked) {
      + .checkbox-decorator::before {
        animation: rippleOff;
        .is-focused & {
          // Prevent checkbox animation and ripple effect on page load
          animation: rippleOff $bmd-checkbox-animation-ripple;
        }
      }

      + .checkbox-decorator .check::after {
        animation: rippleOff $bmd-checkbox-animation-ripple forwards; // Ripple effect on uncheck
      }
    }

    &[disabled],
    fieldset[disabled] & {
      + .checkbox-decorator .check::after,
      .check::after {
        background-color: $gray-dark;
        transform: rotate(-45deg);
      }
      + .checkbox-decorator .check,
      .check {
        border-color: $bmd-checkbox-border-color-disabled;
      }
    }
  }
}

@keyframes checkbox-on {
  0% {
    box-shadow: 0 0 0 10px,
    10px -10px 0 10px,
    32px 0 0 20px,
    0 32px 0 20px,
    -5px 5px 0 10px,
    15px 2px 0 11px;
  }
  50% {
    box-shadow: 0 0 0 10px,
    10px -10px 0 10px,
    32px 0 0 20px,
    0 32px 0 20px,
    -5px 5px 0 10px,
    20px 2px 0 11px;
  }
  100% {
    box-shadow: 0 0 0 10px,
    10px -10px 0 10px,
    32px 0 0 20px,
    0 32px 0 20px,
    -5px 5px 0 10px,
    20px -12px 0 11px;
  }
}

@keyframes checkbox-off {
  0% {
    box-shadow: 0 0 0 10px,
    10px -10px 0 10px,
    32px 0 0 20px,
    0 32px 0 20px,
    -5px 5px 0 10px,
    20px -12px 0 11px,
    0 0 0 0 inset;
  }
  25% {
    box-shadow: 0 0 0 10px,
    10px -10px 0 10px,
    32px 0 0 20px,
    0 32px 0 20px,
    -5px 5px 0 10px,
    20px -12px 0 11px,
    0 0 0 0 inset;
  }
  50% {
    width: 0;
    height: 0;
    margin-top: -4px;
    margin-left: 6px;
    box-shadow: 0 0 0 10px,
    10px -10px 0 10px,
    32px 0 0 20px,
    0 32px 0 20px,
    -5px 5px 0 10px,
    15px 2px 0 11px,
    0 0 0 0 inset;
    transform: rotate(45deg);
  }
  51% {
    width: 20px;
    height: 20px;
    margin-top: -2px;
    margin-left: -2px;
    box-shadow: 0 0 0 0,
    0 0 0 0,
    0 0 0 0,
    0 0 0 0,
    0 0 0 0,
    0 0 0 0,
    0 0 0 10px inset;
    transform: rotate(0deg);
  }
  100% {
    width: 20px;
    height: 20px;
    margin-top: -2px;
    margin-left: -2px;
    box-shadow: 0 0 0 0,
    0 0 0 0,
    0 0 0 0,
    0 0 0 0,
    0 0 0 0,
    0 0 0 0,
    0 0 0 0 inset;
    transform: rotate(0deg);
  }
}

@keyframes rippleOn {
  0% {
    opacity: 0;
  }
  50% {
    opacity: 0.2;
  }
  100% {
    opacity: 0;
  }
}

@keyframes rippleOff {
  0% {
    opacity: 0;
  }
  50% {
    opacity: 0.2;
  }
  100% {
    opacity: 0;
  }
}