mdb-ui-kit/scss/includes/_checkboxes.scss

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

  // Hide native checkbox
  input[type=checkbox] {
    opacity: 0;
    position: absolute;
    margin: 0;
    z-index: -1;
    width: 0;
    height: 0;
    overflow: hidden;
    left: 0;
    pointer-events: none;
  }

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

    .check {
      position: relative;
      display: inline-block;
      width: $mdb-checkbox-size;
      height: $mdb-checkbox-size;
      border: $border-radius-base solid $mdb-checkbox-border-color;
      overflow: hidden;
      z-index: 1;
    }
    .check:before {
      position: absolute;
      content: "";
      transform: rotate(45deg);
      display: block;
      margin-top: -4px;
      margin-left: 6px;
      width: 0;
      height: 0;
      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;
      animation: checkbox-off $mdb-checkbox-animation-check forwards;
    }
  }

  input[type=checkbox] {

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

    &:checked {

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

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

      & + .checkbox-decorator:before {
        animation: rippleOn $mdb-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 $mdb-checkbox-animation-ripple forwards; // Ripple effect on check
      }
    }

    &:not(:checked) {
      & + .checkbox-decorator:before {
        animation: rippleOff $mdb-checkbox-animation-ripple;
      }

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

      }
    }
  }

  // Style for disabled inputs
  fieldset[disabled] &,
  fieldset[disabled] & input[type=checkbox],
  input[type=checkbox][disabled]:not(:checked) ~ .checkbox-decorator .check:before,
  input[type=checkbox][disabled]:not(:checked) ~ .checkbox-decorator .check,
  input[type=checkbox][disabled] + .radio-decorator {
    opacity: 0.5;
  }
  input[type=checkbox][disabled] + .checkbox-decorator .check:after {
    background-color: $mdb-text-color-primary;
    transform: rotate(-45deg);
  }
}

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

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

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