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

html, body {
  height: 100%;
  width: 100%;
}

body {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
}

.smiley {
  font-size: clamp(4rem, 25vw, 20rem);
  line-height: 1;
}

@media (max-width: 768px) {
  .smiley {
    font-size: clamp(12rem, 85vw, 40rem);
  }
}