SOURCE

<div class="container">
  <div class="swal-icon swal-icon--success">
    <span class="swal-icon--success__line swal-icon--success__line--long"></span>
    <span class="swal-icon--success__line swal-icon--success__line--tip"></span>

    <div class="swal-icon--success__ring"></div>
    <div class="swal-icon--success__hide-corners"></div>
  </div>
</div>

.container {
    position: relative;
    width: 100px;
    height: 100px;
    background: #fff;
    overflow: hidden;
    transform: scale(0.8);
  }
.swal-icon {
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%,-50%);
  width: 80px;
  height: 80px;
  border-width: 4px;
  border-style: solid;
  border-radius: 50%;
  position: relative;
}

.swal-icon--success {
  border-color: #a5dc86;
  &:after {
    content: "";
    border-radius: 50%;
    position: absolute;
    width: 60px;
    height: 120px;
    background: #fff;
    transform: rotate(45deg);
  }
  &:before {
    content: "";
    border-radius: 50%;
    position: absolute;
    width: 60px;
    height: 120px;
    background: #fff;
    transform: rotate(45deg);
    border-radius: 120px 0 0 120px;
    top: -7px;
    left: -33px;
    transform: rotate(-45deg);
    transform-origin: 60px 60px;
  }
  &:after {
    border-radius: 0 120px 120px 0;
    top: -11px;
    left: 30px;
    transform: rotate(-45deg);
    transform-origin: 0 60px;
    animation: rotatePlaceholder 4.25s ease-in;
  }
}

.swal-icon--success__ring {
  width: 80px;
  height: 80px;
  border: 4px solid hsla(98, 55%, 69%, 0.2);
  border-radius: 50%;
  box-sizing: content-box;
  position: absolute;
  left: -4px;
  top: -4px;
  z-index: 2;
}

.swal-icon--success__hide-corners {
  width: 5px;
  height: 90px;
  background-color: #fff;
  padding: 1px;
  position: absolute;
  left: 28px;
  top: 8px;
  z-index: 1;
  transform: rotate(-45deg);
}

.swal-icon--success__line {
  height: 5px;
  background-color: #a5dc86;
  display: block;
  border-radius: 2px;
  position: absolute;
  z-index: 2;
}

.swal-icon--success__line--tip {
  width: 25px;
  left: 14px;
  top: 46px;
  transform: rotate(45deg);
  animation: animateSuccessTip 0.75s;
}

.swal-icon--success__line--long {
  width: 47px;
  right: 8px;
  top: 38px;
  -webkit-transform: rotate(-45deg);
  transform: rotate(-45deg);
  animation: animateSuccessLong 0.75s;
}

@keyframes rotatePlaceholder {
  0% {
    -webkit-transform: rotate(-45deg);
    transform: rotate(-45deg);
  }

  5% {
    -webkit-transform: rotate(-45deg);
    transform: rotate(-45deg);
  }

  12% {
    -webkit-transform: rotate(-405deg);
    transform: rotate(-405deg);
  }

  to {
    -webkit-transform: rotate(-405deg);
    transform: rotate(-405deg);
  }
}


@keyframes animateSuccessTip {
  0% {
    width: 0;
    left: 1px;
    top: 19px;
  }

  54% {
    width: 0;
    left: 1px;
    top: 19px;
  }

  70% {
    width: 50px;
    left: -8px;
    top: 37px;
  }

  84% {
    width: 17px;
    left: 21px;
    top: 48px;
  }

  to {
    width: 25px;
    left: 14px;
    top: 45px;
  }
}


@keyframes animateSuccessLong {
  0% {
    width: 0;
    right: 46px;
    top: 54px;
  }

  65% {
    width: 0;
    right: 46px;
    top: 54px;
  }

  84% {
    width: 55px;
    right: 0;
    top: 35px;
  }

  to {
    width: 47px;
    right: 8px;
    top: 38px;
  }
}