<div class="buttons">
  <button class="blob-btn">
    Blob Button
    <span class="blob-btn__inner">
      <span class="blob-btn__blobs">
        <span class="blob-btn__blob"></span>
        <span class="blob-btn__blob"></span>
        <span class="blob-btn__blob"></span>
        <span class="blob-btn__blob"></span>
      </span>
    </span>
  </button>
  <br/>

<svg xmlns="http://www.w3.org/2000/svg" version="1.1">
  <defs>
    <filter id="goo">
      <feGaussianBlur in="SourceGraphic" result="blur" stdDeviation="10"></feGaussianBlur>
      <feColorMatrix in="blur" mode="matrix" values="1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 21 -7" result="goo"></feColorMatrix>
      <feBlend in2="goo" in="SourceGraphic" result="mix"></feBlend>
    </filter>
  </defs>
</svg>
*, *:before, *:after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}
$openSans: 'Open Sans', Helvetica, Arial, sans-serif;
body {
  background: #333;
  font-family: $openSans;
}

.buttons {
  margin-top: 50px;
  text-align: center;
  border-radius:30px;
}

$cyan: #0505A9;
$dark: #FFFFFF;
$borderW: 2px;

.blob-btn {
  $numOfBlobs: 4;
  z-index: 1;
  position: relative;
  padding: 20px 46px;
  margin-bottom: 30px;
  text-align: center;
  text-transform: uppercase;
  color: $cyan;
  font-size: 16px;
  font-weight: bold;
  background-color: transparent;
  outline: none;
  border: none;
  transition: color 0.5s;
  cursor: pointer;
  border-radius:30px;
  
  &:before {
    content: "";
    z-index: 1;
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    border: $borderW solid $cyan;
    border-radius:30px;
  }
  
  &:after {
    content: "";
    z-index: -2;
    position: absolute;
    left: $borderW*1.5;
    top: $borderW*1.5;
    width: 100%;
    height: 100%;

    transition: all 0.3s 0.2s;
    border-radius:30px;
  }
  
  &:hover {
    color: $dark;
    border-radius:30px;
    
    &:after {
      transition: all 0.3s;
      left: 0;
      top: 0;
      border-radius:30px;
    }
  }
  
  &__inner {
    z-index: -1;
    overflow: hidden;
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    border-radius:30px;
    background:#ffffff;
  }
  
  // additional container created, because in FF blobs are breaking overflow:hidden of element with svg gooey filter
  &__blobs {
    position: relative;
    display: block;
    height: 100%;
    filter: url('#goo');
  }
  
  &__blob {
    position: absolute;
    top: $borderW;
    width: 100% / $numOfBlobs;
    height: 100%;
    background: $cyan;
    border-radius: 100%;
    transform: translate3d(0,150%,0) scale(1.7);
    transition: transform 0.45s;
    
    @supports(filter: url('#goo')) {
      transform: translate3d(0,150%,0) scale(1.4);
    }
    
    @for $i from 1 through $numOfBlobs {
      &:nth-child(#{$i}) {
        left: ($i - 1) * (120% / $numOfBlobs);
        transition-delay: ($i - 1) * 0.08s;
      }
    }
    
    .blob-btn:hover & {
      transform: translateZ(0) scale(1.7);
      
      @supports(filter: url('#goo')) {
        transform: translateZ(0) scale(1.4);
      }
    }
  }
  
}

External CSS

  1. https://fonts.googleapis.com/css?family=Open+Sans

External JavaScript

This Pen doesn't use any external JavaScript resources.