Create a CSS pulse effect from border outwards

Question

I started creating a code pen with the effect I want here: https://codepen.io/oli_js/pen/KKPGZLm?editors=1100

However, this pulse effect radiates out from the centre point, but I want the inner circle to be transparent and just have the effect radiate just from the border.

Does anyone know of any any magical CSS wizardry to do this?!

.pulse {
    border-radius: 50px;
    height: 80px;
    left: 50%;
    letter-spacing: 0.05em;
    line-height: 50px;
    position: absolute;
    text-align: center;
    text-transform: uppercase;
    top: 50%;
    width: 80px;
}

.pulse:after {
    -webkit-animation: pulse 2s infinite linear;
    background: red;
    border-radius: 50px;
    content: '';
    height: 100%;
    left: 0;
    opacity: 0;
    position: absolute;
    top: 0;
    width: 100%;
}

.button {
    background: transparent;
    border-radius: 100% 100%;
      width: 40px;
    height: 40px;
    left: 50%;
    border:2px solid red;
    position: absolute;
    top: 50%;
    transform: translate(-50%, -50%);
}

@-webkit-keyframes pulse{
  0% {transform:scale(0.5);
    opacity:0;}
  33% {transform:scale(0.8);
    opacity:1;}
  100% {transform:scale(1);
    opacity:0;}
}

<div class="pulse">
  <div class="button"> </div>
</div>

Answer 1

You can do it with shadow effect too like this..

   .ripple{
  display: block;
  width: 30px;
  height: 30px;
  border-radius: 50%;
  border:2px red solid;
  animation: pulse 2s infinite;
}

@-webkit-keyframes pulse {
  0% {
    -webkit-box-shadow: 0 0 0 0 rgba(255,0,0, 0.4);
  }
  70% {
      -webkit-box-shadow: 0 0 0 10px rgba(255,0,0, 0);
  }
  100% {
      -webkit-box-shadow: 0 0 0 0 rgba(255,0,0, 0);
  }
}

   <div class="ripple"></div>