<button>Get started</button>

@import url('https://fonts.googleapis.com/css?family=Space%20Grotesk:700|Space%20Grotesk:400');

:root {
/*  change this for scaling  */
  --m: 4rem;
  
  --red: #FF6565;
  --pink: #FF64F9;
  --purple: #6B5FFF;
  --blue: #4D8AFF;
  --green: #5BFF89;
  --yellow: #FFEE55;
  --orange: #FF6D1B;
  
}
body {
  background-color: #141516;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
}

button {
  border: calc(0.08 * var(--m)) solid transparent;
  position: relative;
  color: #F3F3F3;
  font-family: 'Space Grotesk';
  font-size: var(--m);
  border-radius: calc(0.7 * var(--m));
  padding: calc(0.5 * var(--m)) calc(1 * var(--m));
  display: flex;
  justify-content: center;
  cursor: pointer;
  
  background:linear-gradient(#121213, #121213), linear-gradient(#121213 50%, rgba(18, 18, 19, 0.6) 80%, rgba(18, 18, 19, 0)),  linear-gradient(90deg, var(--orange), var(--yellow), var(--green), var(--blue), var(--purple), var(--pink), var(--red));
  background-origin: border-box;
  background-clip: padding-box, border-box, border-box;
  background-size: 200%;
  animation: animate 2s infinite linear;
}

button::before {
  content: '';
  background: linear-gradient(90deg, var(--orange), var(--yellow), var(--green), var(--blue), var(--purple), var(--pink), var(--red));
  height: 30%;
  width: 60%;
  position: absolute;
  bottom: -20%;
  z-index: -5;
  background-size: 200%;
  animation: animate 2s infinite linear;
  filter: blur(calc(0.8 * var(--m)));
}

button:hover, button:hover::before {
  animation: animate 0.5s infinite linear;
}

@keyframes animate {
  0% {background-position: 0}
  100% {background-position: 200%}
}

@media screen and (max-width: 1000px) {
  :root {
    --m: 2rem;
  }
}

// no js but if you liked this pen, give it a heart <3