style.css

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

body {
  display: grid;
  place-items: center;
  min-height: 100vh;
  background-color: #191a21;
}

button {
  padding: 1rem 2rem;
  border-radius: 10rem;
  border: none;
  background-color: transparent;
  color: #fff;
  font-size: 1.2rem;
  position: relative;
  overflow: hidden;
}

button::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0;
  width: 2rem;
  height: 2rem;
  background-color: #fff;
  transform: translate(-50%, -50%);
  border-radius: 50%;
  filter: blur(12px);
  animation: button-animation 3s linear infinite;
}

button::after {
  content: attr(data-text);
  position: absolute;
  top: 2%;
  left: 1%;
  width: 98%;
  height: 96%;
  background-color: #252731;
  border-radius: inherit;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
}

button:hover::after {
  background-image: linear-gradient(to top, rgb(44, 44, 44), #252731);
}

@keyframes button-animation {
  0% {
    left: 0;
    top: 0;
  }

  35% {
    left: 100%;
    top: 0;
  }

  50% {
    left: 100%;
    top: 100%;
  }

  85% {
    left: 0%;
    top: 100%;
  }
}