style.css

@import url("https://fonts.googleapis.com/css?family=Montserrat:400,700");

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  background-color: #131217;
  width: 100%;
  height: 100vh;
  position: relative;
  display: grid;
  place-content: center;
  font-family: Montserrat;
  overflow: hidden;
}

h1 {
  font-size: 8rem;
  font-weight: 700;
  color: white;
  position: relative;
  z-index: 2;
  text-align: center;
}

#pattern {
  position: absolute;
  top: -44px;
  left: -50px;
  right: 0;
  bottom: 0;
}

#gradient {
  background: radial-gradient(#ff8811, transparent 50%);
  width: 400px;
  height: 400px;
  position: absolute;
  top: -200px;
  left: -200px;
  transform: translate(200px, 200px);
}

button {
  position: relative;
  padding: 1rem 3rem;
  background: linear-gradient(to bottom right, #ff8811, #dd2d4a);
  border: none;
  cursor: pointer;
  margin: 25px;
}

button > span {
  font-family: Montserrat;
  font-size: 1.5rem;
  font-weight: 700;
  color: white;
  position: relative;
  z-index: 1;
}

button:after {
  content: "";
  position: absolute;
  left: 4px;
  top: 4px;
  right: 4px;
  bottom: 4px;
  background-color: #131217;
  transition: opacity 0.4s;
  opacity: 0;
}

button:before {
  content: "";
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  opacity: 0;
  background: linear-gradient(to bottom right, #ff8811, #dd2d4a);
  filter: blur(20px);
  transition: opacity 0.4s;
  animation: scale 2s ease-in-out infinite alternate forwards;
}

button:hover:after,
button:hover:before {
  opacity: 1;
}

@keyframes scale {
  from {
    transform: scale(1);
  }
  to {
    transform: scale(1.1);
  }
}