<!-- 
autor: Marco Barría 
https://twitter.com/marco_bf
-->

<a href="#" class="btn-mix-noborder" data-text="color">color</a>
<a href="#" class="btn-mix" data-text="codepen">codepen</a>
<a href="#" class="btn-mix-noRadius" data-text="marco">marco</a>

$bg-color: #222;

[class*="btn-"] {
  outline:0;
  border-radius: 50px;
  font-size: 0.8em;
  font-family: 'Roboto', sans-serif;
  font-weight: 400;
  letter-spacing: 4px;
  overflow: hidden;
  position: relative; //absolute
  padding: 2em 3em;
  margin: 4em;
  text-transform: uppercase;
  -webkit-tap-highlight-color: transparent;
  transition: all 500ms ease-in-out;
  &::after, &::before { 
    content: "";
    position: absolute;
  }
  &:hover, &:focus {
    background: rgba(255, 255, 255, 0.8);
  }
}

[class*="btn-mix"] {
  &::after {
    background: $bg-color;
    border-radius: 120px;
    content: attr(data-text);
    color: #fff;
    padding: 1.6em 2.5em;
    top: 0.4em;
    left: 0.5em;
    -moz-user-select: none;
    user-select: none;
    user-drag: none;
  }
  &::before {
    background: transparent;
    border-radius: 100%;
    top: 50%;
    left: 50%;
    box-shadow: 0 1em 2em 3em rgba(255, 50, 0, 0.5),
                4em 0em 2em 2em rgba(155, 50, 0, 0.6),
                -4em -2em 2em 2em rgba(255, 0, 150, 0.5),
                -4em 2em 2em 4em rgba(0, 0, 150, 0.5),
                0 -3em 2em 3em rgba(120, 250, 0, 0.5),
                2em -1em 2em 2em rgba(50, 10, 200, 0.5);
    width: 0;
    height: 0;
    animation: mix 5s linear infinite;
  }
}

@keyframes mix {
  
  30% {
    box-shadow: 0 -1em 2em 3em rgba(255, 0, 200, 0.5),
                4em -1em 2em 3em rgba(255, 50, 0, 0.8),
                -4em 2em 3em 2em rgba(155, 200, 0, 0.5),
                -4em -2em 2em 2em rgba(200, 0, 150, 0.6),
                0 3em 2em 2em rgba(20, 250, 0, 0.5),
                2em 1em 2em 2em rgba(50, 10, 250, 0.5);
  }
  
  60% {
    box-shadow: 2em 1em 2em 3em rgba(55, 0, 200, 0.5),
                3em 1em 2em 3em rgba(25, 150, 0, 0.6),
                3em -2em 3em 3em rgba(155, 200, 0, 0.5),
                -4em 2em 2em 3em rgba(200, 0, 50, 0.6),
                0 -3em 2em 3em rgba(200, 250, 0, 0.5),
                -2em 1em 2em 3em rgba(50, 210, 250, 0.6);
  }

}

.btn-mix-noborder {
  &::after {
    background: transparent !important;
    color: $bg-color !important;
  }
}

.btn-mix-noRadius {
  border-radius: 0 !important;
  &::after, &::before {
    border-radius: 0 !important;
  }
}

html,
body {
  width: 100%;
  height: 100%;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizelegibility;
}

body {
  background: $bg-color;
  display: flex;
  justify-content: center;
  align-items: center; 
}

a {
  text-decoration: none;
}