style.css

@import url("https://fonts.googleapis.com/css2?family=Bungee&display=swap");

:root {
  --gradient: linear-gradient(90deg, #7f7fd5, #86a8e7, #f64f59);
}

* {
  box-sizing: border-box;
}

body {
  font-family: "Bungee", cursive;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
  overflow: hidden;
  margin: 0;
  font-size: 1.125em;
  line-height: 1.6;
  background: #7f7fd5;
  /* we are playing with background-position since background-image doesn't support transitions */
  background-size: 300%;
  background-image: var(--gradient);
  animation: bg-animation 20s infinite alternate;
}

@keyframes bg-animation {
  0% {
    background-position: left;
  }
  100% {
    background-position: right;
  }
}

.container {
  background: #fff;
  width: 70vw;
  padding: 3rem;
  box-shadow: 0 0 3rem rgba(0, 0, 0, 0.15);
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
}

.title {
  margin: 1rem;
  padding: 1rem;
  text-align: center;
  text-transform: uppercase;
  font-weight: 900;
  font-style: italic;
  font-size: 3rem;
  color: #7f7fd5;
  line-height: 0.8;
  background-image: var(--gradient);
  background-clip: text;
  -webkit-background-clip: text;
  color: transparent;
  -webkit-text-fill-color: transparent;
  background-size: 300%;
  transition: background-position 1s;
}

.title:hover {
  background-position: right;
}

.btn {
  color: #fff;
  font: inherit;
  border: 0;
  cursor: pointer;
  padding: 0.5rem 1.25rem;
  background: var(--gradient);
  background-size: 300%;
  background-position: left;
  transition: background-position 350ms;
}

.btn:hover {
  background-position: right;
}