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

@mixin radio-color($color, $opacity) {
  & ~ .check,
  & ~ .radio-decorator {
    opacity: $opacity;
  }

  & ~ .check {
    background-color: $color;
  }

  & ~ .radio-decorator {
    border-color: $color;
  }
}

label.radio,
label.radio-inline,
.radio label,
.radio-inline label {
  cursor: pointer;
  padding-left: 45px;
  position: relative;
  color: $mdb-radio-label-color;

  span {
    display: block;
    position: absolute;
    left: 10px;
    top: 2px;
    transition-duration: 0.2s;
  }
  .radio-decorator {
    border: 2px solid $mdb-radio-color-off;
    height: 15px;
    width: 15px;
    border-radius: 100%;
  }
  .check {
    display: inline-block;
    height: 15px;
    width: 15px;
    border-radius: 100%;
    background-color: $mdb-radio-color-on;
    transform: scale3d(0, 0, 0);
  }
  .check:after {
    display: block;
    position: absolute;
    content: "";
    background-color: $mdb-text-color-primary;
    left: -18px;
    top: -18px;
    height: 50px;
    width: 50px;
    border-radius: 100%;
    z-index: 1;
    opacity: 0;
    margin: 0;
    transform: scale3d(1.5, 1.5, 1);
  }
  input[type=radio]:not(:checked) ~ .check:after {
    animation: rippleOff 500ms;
  }
  input[type=radio]:checked ~ .check:after {
    animation: rippleOn 500ms;
  }

  input[type=radio] {
    opacity: 0;
    height: 0;
    width: 0;
    overflow: hidden;

    &:checked {
      @include radio-color($mdb-radio-color-on, 1);
    }
    &:checked ~ .check {
      transform: scale3d(0.55, 0.55, 1);
    }
  }

  input[type=radio][disabled] {

    // light theme spec: Disabled: #000000, Opacity  26%
    @include radio-color($black, 0.26);

    // dark theme spec: Disabled: #FFFFFF, Opacity  30%
    .theme-dark & {
      @include radio-color($white, 0.30);
    }
  }
}


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

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