#container
  button.btn#btn-1
    span Blur on hover
  
  button.btn#btn-2
    span Clear on hover

$blur: 4px;
$max: 870px;
$min: 0px;
$url: 'https://images.unsplash.com/photo-1458682625221-3a45f8a844c7?ixlib=rb-0.3.5&q=85&fm=jpg&crop=entropy&cs=srgb&ixid=eyJhcHBfaWQiOjE0NTg5fQ&s=71fe1cccc16ab8dbd431de076c68802b';

*, *:before, *:after {
  box-sizing: inherit;
}

html,body {
  width: 100%;
  height: 100%;
  overflow: hidden;
  box-sizing: border-box;
}

#container {
  width: 100%;
  height: 100%;
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 32px;
  position: relative;
  text-align: center;
  background: url($url) no-repeat center;
  background-size: cover;
}

.btn {
  width: 280px;
  height: 56px;
  flex-shrink: 0;
  margin: 0 auto;
  position: relative;
  overflow: hidden;
  background: transparent;
  border: 2px solid white;
  color: white;
  font-family: Roboto,sans-serif;
  font-size: 18px;
  letter-spacing: 0.8px;
  text-transform: uppercase;
  cursor: pointer;
  &:focus { outline: none; }

  &:before {
    content: "";
    padding: 100%;
    background: url($url) no-repeat;
    background-size: cover;
    background-attachment: fixed;
    background-position: 50%;
  }
  
  span {
    position: absolute;
    top: 50%;
    right: 0;
    left: 0;
    transform: translateY(-50%);
    z-index: 9;
  }
  
  &#btn-1 {
    &:before {
      transition: all 0.3s ease;
    }

    &:hover:before {
      -webkit-filter: blur($blur);
      filter: blur($blur);
    }
  }
  
  &#btn-2 {
    &:before {
      transition: all 0.3s ease;
      -webkit-filter: blur($blur);
      filter: blur($blur);
    }

    &:hover:before {
      -webkit-filter: blur(0);
      filter: blur(0);
    }
  }
}