styles.css

@font-face {
  font-family: "Raleway";
  src: url("./Raleway-Black.ttf");
}

* {
  box-sizing: border-box;
}

:root {
  --text-color: #ff4dd2;
  --bg-color: #00ffcc;
}

body {
  background-color: var(--bg-color);
  font-family: "Raleway", sans-serif;

  display: grid;
  place-items: center;
  margin: 0;

  height: 100dvh;
}

#rule {
  font-size: clamp(1.75rem, 8vw + 0rem, 4rem);
  max-width: 800px;

  color: var(--text-color);

  text-align: justify;
  text-transform: uppercase;

  border: 0.2em solid var(--text-color);

  border-radius: 5px;
  padding: 1em;
}

span:nth-child(n + 5):nth-child(-n + 6),
span:nth-child(n + 13):nth-child(-n + 14) {
  position: relative;
}

span:nth-child(n + 5):nth-child(-n + 6)::after,
span:nth-child(n + 13):nth-child(-n + 14)::after {
  content: "";
  display: inline-block;

  position: absolute;
  top: 0;
  left: 0;

  width: 110%;
  height: 100%;

  opacity: 0;
  background: var(--bg-color);

  animation: strike 2s linear 0.2s 1 normal forwards;
}

@keyframes strike {
  0%,
  100% {
    opacity: 0.9;
    width: 0;
  }

  100% {
    opacity: 0.9;
    width: 110%;
  }
}